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building error of assemblyInfo.cd could not be found in visual studio 2012 on win 7

After searching the SO forum, I cannot find a working solution for my question. If you find one, I would really appreciate it.
In Visual Studio 2012, I am building a C# project. I get the following error:
Source file 'Properties\Assemblyinfo.cs' could not be found.
I have this solution:
Source file 'Properties\AssemblyInfo.cs' could not be found
But, it does not work for me.
Actually, I have the 'Assemblyinfo.cs' in working directory, I can see it in VS solution explorer.

Have you tried deleting the assemblyinfo.cs files and then trying Clean and Rebuild solution? If you don't need versioning this might help you.

Have you tried a Clean Solution, followed by a Rebuild Solution?
The AssemblyInfo.cs file should be recreated on a build.

I got this error even after I tried to Clean and Build. I could also could see the AssemblyInfo.cs file. I found out that the build was interacting with a power shell script(not entirely sure how) in the solution directory.
Long story short, Every project, except the one I had added(where the problem was), was mentioned in that script. I added the missing info to that script and I could build again.
I doubt your case will be exactly the same, but I imagine there could be some script or something similar that handles/references all the projects, except the one where your problem persist. Try searching the files for the text of project names.

I have encountered this situation.
I find out why. It is usually due to confusion between mscorlib.dll versions.
There are two ways:
Change assemblyinfo version from 1.0.0.0 to 1.* (change value to *). See link:
MSBuild extensions AssemblyInfo fails with version number not valid
Get an error when trying to set the build version with the AssemblyInfo Task
The second way is simple, I have applied it successfully, that is reinstalling .Net Framework 3.5.

Clean and Rebuild did not help for me.
What helped was manually deleting ALL /obj and /bin files and then using Clean and Rebuild.

Visual studio - getting error "Metadata file 'XYZ' could not be found" after edit continue

I have stumbled into an issue that is really annoying.
When I debug my software, everything runs OK, but if I hit a breakpoint and edit the code, when I try to continue running I get an error:
Metadata file 'XYZ' could not be found
After looking around for a while, I found some a similar issues, but they were all regarding a build failure, which is not my case (this happens only after edit-continue).
What I have tried so far:
My code is compiling and running.
I cleaned the solution and restarted VS.
I made sure that the missing file's project is being build for the configuration I am running (in configuration manager).
I manually built the missing file's project.
Some extra info:
It does not matter what I change, still get the same error (the change is not related to the missing file).
This happens also when I pause and continue (not only breakpoints)
I am running the project using a custom configuration (configuration manager...). When I run it using the default Debug configuration the error does not occur.
Any ideas?

Eventually what solved the issue was:
Clean every project individually (Right click> Clean).
Rebuild every project individually (Right click> Rebuild).
Rebuild the startup project.
I guess for some reason, just cleaning the solution had a different effect than specifically cleaning every project individually.
Edit:
As per #maplemale comment, It seems that sometimes removing and re-adding each reference is also required.
Update 2019:
This question got a lot of traffic in the past, but it seems that since VS 2017 was released, it got much less attention.
So another suggestion would be - Update to a newer version of VS (>= 2017) and among other new features this issue will also be solved

As far as I can tell, this happens when the project dependencies gets messed up for whatever reason (whilst all the inter-project references are still intact). For many cases, it is NOT a code issue. And for those who have more than a few projects, going through them one at a time is NOT acceptable.
It's easy to reset project dependencies -
Select all projects and right click unload
Select all projects and right click reload
Rebuild solution
For those who have an issue in their code or some other issue that's causing this problem you'll obviously have to solve that issue first.

One possible reason could be you have upgraded the some of your projects (in the solution) to higher version e.g. from .NET 4.0 to 4.5 This happened in my case when I opened the solution in VS 2013 (originally created using VS 2010 and .NET 4.0). When I opened in VS 2013 my C++ project got updated to .NET 4.5 and I started to see the problem.

Generally this kind of error comes with human mistakes like if we change the namespace in some improper way, or changing folder names from explorer for current project etc, where compiler is unable to detect sometimes.
I came across the same error, to resolve which I tried few steps. Please follow all the steps :
Clean whole Solution
Right Click on every Project in your solution , Go to Properties and make your Default namespace as well as Default assembly name same as in your code (i.e namespace before class name)
Check Folder names for each project by going through the explorer(Where your project solution is). If not matching with your project names, make it similar (Like step 2) to them.
Remove all your references from each project relevant to another of same solution, and add it again.
In Your Project Solution folder, you will find Visual c# Project file. Right click and open with Notepad. In your initial lines you would find for lines for every project like below:
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "**Client**", "**Client** \ **Client**.csproj", "{4503E259-0E3B-414A-9074-F251684322A5}"
EndProject
Check again Foldernames (I have highlighted in BOLD) and make it similar to what you did in step 2.
Clean the whole solution again
Build The Solution (If doesn't work try building individual after cleaning again)

Make sure all your dependent projects are using the same .Net Framework version. I had the same issue caused by a dependent project using 4.5.1, while all others were using 4.5. Changing the project from 4.5.1 to 4.5 and rebuilding my solution fixed this issue for me.

XYZ couldn't be found because is not built yet....
Right click on the solution and check Project Dependencies, the Project Build Order should also change according to the dependencies that have been set.

The only thing that worked for me was to delete the Solution User Options (.suo) file. Note that, this is a hidden file.
To locate this file, close your Virsual studio and search for .suo from the file explorer within your project.
PS: a new .suo file will be created again when you rebuild your project and hopefully this newly created one wont give you issues.
I hope that helps someone get rid of this anoying error :).

I had this problem for days! I tried all the stuff above, but the problem kept coming back. When this message is shown it can have the meaning of "one or more projects in your solution did not compile cleanly" thus the metadata for the file was never written. But in my case, I didn't see any of the other compiler errors!!! I kept working at trying to compile each solution manually, and only after getting VS2012 to actually reveal some compiler errors I hadn't seen previously, this problem vanished.
I fooled around with build orders, no build orders, referencing debug dlls (which were manually compiled)... NOTHING seemed to work, until I found these errors which did not show up when compiling the entire solution!!!!
Sometimes, it seems, when compiling, that the compiler will exit on some errors... I've seen this in the past where after fixing issues, subsequent compiles show NEW errors. I don't know why it happens and it's somewhat rare for me to have these issues. However, when you do have them like this, it's a real pain in trying to find out what's going on. Good Luck!

Well, my answer is not just the summary of all the solutions, but it offers more than that.
Section (1):
In general solutions:
I had 4 errors of this kind (‘metadata file could not be found’) along with 1 error saying 'Source File Could Not Be Opened (‘Unspecified error ‘)'.
I tried to get rid of ‘metadata file could not be found’ error. For that, I read many posts, blogs etc and found these solutions may be effective (summarizing them over here):
Restart VS and try building again.
Go to 'Solution Explorer'. Right click on Solution. Go to Properties. Go to 'Configuration Manager'. Check if the checkboxes under 'Build' are checked or not. If any or all of them are unchecked, then check them and try building again.
If the above solution(s) do not work, then follow sequence mentioned in step 2 above, and even if all the checkboxes are checked, uncheck them, check again and try to build again.
Build Order and Project Dependencies:
Go to 'Solution Explorer'. Right click on Solution. Go to 'Project Dependencies...'. You will see 2 tabs: 'Dependencies' and 'Build Order'. This build order is the one in which solution builds. Check the project dependencies and the build order to verify if some project (say 'project1') which is dependent on other (say 'project2') is trying to build before that one (project2). This might be the cause for the error.
Check the path of the missing .dll:
Check the path of the missing .dll. If the path contains space or any other invalid path character, remove it and try building again.
If this is the cause, then adjust the build order.

Are you using a database code generation tool like SQLMETAL in your project?
If so, you may be facing a pluralized to unpluralized transition issue.
In my case, I have noted that some old pluralized (*) table names (upon which SQLMETAL adds, by default, an "s" letter at the end) table references to classes generated by SQLMETAL.
Since, I have recently disabled Pluralization of names, after regerating some database related classes, some of them lost their "s" prefix. Therefore, all references to affected table classes became invalid. For this reason, I have several compilation errors like the following:
'xxxx' does not contain a definition for 'TableNames' and no extension method 'TableNames' accepting a first argument of type 'yyyy' could be found (are you missing a using directive or an assembly reference?)
As you know, I takes only on error to prevent an assembly from compiling. And that is the missing assemply is linkable to dependent assemblies, causing the original "Metadata file 'XYZ' could not be found"
After fixing affected class tables references manually to their current names (unpluralized), I was finnaly able to get my project back to life!
(*) If option Visual Studio > Tools menu > Options > Database Tools > O/R Designer > Pluralization of names is enabled, some SQLMETALl code generator will add an "s" letter at the end of some generated table classes, although table has no "s" suffix on target database. For further information, please refer to http://msdn.microsoft.com/en-us/library/bb386987(v=vs.110).aspx
Hope it helps!

I had this error come up. I followed all of the solutions here but nothing worked. I was using Visual Studio 2013 Professional. I couldn't get the individual project rebuilds to work and I finally figured out there was a circular dependency in my references. Visual Studio does a pretty good job normally of warning you if you are adding a reference to something that references back, but for some reason it didn't in this instance. I added a reference to a project that referenced the project I was working on - and it accepted it. VS bug perhaps?

My 5 cents.
This problem started after a solution wide clean.
I managed to get the problem to go away by setting the Active Solution configuration in: Build -> Configuration manager to release. Then build and set it back to debug again. The build succeeded after that.

Close VS, locate and remove the 'packages' folder from outside of visual studio. Restart VS and build -> all dependencies are reinstalled

Visual Studio 2019 Community 16.3.10
I had similar issue with Release build. Debug build was compiling without any issues.
Turns out that the problem was caused by OneDrive. Most likely one could experience similar issues with any backed-up drive or cloud service.
I cleaned everything as per Avi Turner's great answer.
In addition, I manually deleted the \obj\Release -folder from my OneDrive folder and also logged to OneDrive with a browser and deleted the folder there also to prevent OneDrive from loading the cloud version back when compiling.
After that rebuilt and everything worked as should.

this happens because of the difference of names in the folder name and namespace name. If u create a namespace in a certain name , and later you rename it the namespace will have the old name itself. And the compilation will take the old path to find the .dll and .exe file . To avoid this open the .csproj file of each namespace with a text file , and find the old path in the file.
remove this, clean and rebuild the solution. This worked for me. I spent an entire day working on this problem.

I had this and managed to fix it using this SO answer:
Metadata file '.dll' could not be found
I had to uncheck all of the boxes, click Apply, reenable all of the checkboxes and then click apply again, but it fixed the problem.

I just ran into this issue and after an hour of screwing around realized I had added an aspx file to my product that had the same name as one of my Linq-To-Sql classes.
Class and Page where "Queue".
Changed the page to QueueMgr.aspx and everything built just fine.

For a new build, it could be that some dependencies aren't installed. For me it was Crystal Reports.

It happens when one project dll is failing and that is referenced by number of projects. So first fix it and then Build individuals.

I ve had this problem and it has started after importing our solution to TFS as a new project.I came across this topic and found a quick solution with some inspiration from your answers.
All i needed to do is to rebuild the project thats supposedly lost its metadata file and voila , problem solved.

There's also one another silly reason which you should check with patience... as it occurred to me after wasting 4hours searching for answers:
The story to me was that I accidentally changed a small line of code among thousands of c# class files and then trying to rebuild the solution. As you could imagine, I ended up with 40+ meta data file missing errors and with 1 compilation error among them -- which I didn't check carefully, purely thinking all errors were the same!
after 4 hours searching and then accidentally double checking my error list, I found that silly code error, fixed it, compiled, and then error disappeared.
Not a good answer to your problem, but do hope my case wasn't same to yours.

I had the same problem. In my case I had by mistake I had set all the projects apart from the project with the main method as console application.
To resolve I went to every project other than the one with main function and right click> properites > output type > class library

it was happened to me because I've a strange clash in the namespaces:
I had
AssemblyA
with namespace
AssemblyA.ParentNamespace
witch defines ClassA
and in the same assembly another namespace with name
AssemblyA.ParentNamespace.ChildNamespace
witch defines a different ClassA (but with the same name)
I had then in AssemblyA.ParentNamespace IInterfaceB witch had a method that in the beginning returns IEnumerable and a ClassB witch implements IInterfaceB
I had later modified the method in ClassB to return IEnumerable but I've forgot to update the IInterfaceB definition, so the method there was still returning IEnumerable
the fun fact was that the solution still complile if I did a rebuild all, but the tests witch refers AssemblyA didsn't work and returns the "Metadata file could not be found"error.
updating InterfaceB to correctly return IEnumerable as its implementor ClassB did solved the problem, unfortunately the error message was vague and also the fact that the compilation worked makes me suppose that maybe there is something to fix in the compiler

A coworker was running into this problem and the cause was eluding us. Eventually we realized that the project directory (and therefore the path to the NuGet packages) contained %20 (thanks, some Git gui tool which shall not be named) and the error messages showed that the compiler was looking for an very similar-looking path but one which had to %20, rather a space. Apparently something in the build system somewhere performs HTML-decoding on local filesystem paths.
Renamed the working copy directory and everything started working.

I had this issue too.
It started after I did a little folder tidying in my project.
I then tried to compile and got many duplicate class errors. (despite them not being duplicated. I think the linking was just out of wack)
Upon checking these, the errors would all disappear leaving only the "Metadata file ...debug\application.exe could not be found" error.
I solved this by looking in the build output window to find which classes were duplicated.
I would then right click the class name and "go to definition".
there will be two definitions to select from, open them both, the second definition will seem to open the same file again, however the second one will identify as the error source(red underline).
Delete all the code out of the file and save(This will not effect your actual file).
This should now compile correctly.

Ensure that there are no spaces in the path to your project...
I am using Windows 10 with Visual Studio Community 2019 and I was cloning a multi project solution as it was from a GIT repo. I was having this error with all other dependencies in the solution along with a E_POINTER error. Its path, inherited from GIT, had spaces like C:/repos/MY PROJECT NAME/ ...
I deleted it, cloned it again and make sure that its path contained no spaces like C:/repos/MY_PROJECT_NAME/ ...
That fixed my problem.

I had same issue too.
In my case, I recently add an internal class to somewhere in project. One of the dependencies in solution has same class name and both of them are added correctly to references.
I changed my last activity and rebuild, it works.
Be sure that your compiler messages are valid. In my case I catch reference error from there, not listed as an error in Error List.

Visual Studio "Rebuild all failed"

Why does Rebuild fail with no errors?
Since this morning, this error keeps showing up. I build the entire solution (25 C# managed projects) and a "Rebuild All failed" appears, but without any errors! (I have 13 warnings about COM not supporting Generics, but it's "normal" because one dll is exposed as COM.)

Not an answer per se - but you're better off looking at the output window and seeing what it says there.
Also, to help with that you might want to look at your MSBuild verbosity - as shown on this screenshot (last two options):
Beware - the highest level generates a MASSIVE amount of information.
Finally - running msbuild from the solution folder in a command prompt will really nail the issue - because error messages and warnings come up in red and yellow respectively.

I found my own solution and it is simple:
When this error occurs, save the project and close VS 2013. After that, re-open VS2013 and open the last project.
It works like a charm. But it is very annoying every time!
Many people reported this problem in VS2010, VS2012 and VS2013.

Could be a corrupt Solution User Options file.
Close the solution, delete its .suo (.v12.suo for VS2012+), reopen the solution, and Visual Studio will build a new one. You will lose the StartUp Project, breakpoints, bookmarks, which files are open, which projects/folders are expanded, etc. But that's all minor compared to the solution not building!

I had the same problem. I was trying to refrence a higher .net framework version(4.5.2) to lower .net framework version(4.5) which was causing build error. I made the version same in both projects and it worked.

Check the Output Window (View -> Output) as that will tell you what's going wrong. Sometimes a reference might be missing or there is an issue with the targeted version of .NET for one project in a solution.

Have you tried to clean the solution befor rebiuld it?

This is the list of checks & things I would do if I were you (try to build after each step):
Is error list activated? (Sometimes I forgot to activate and I can see only warnings & messages)
Check output window for error messages..
Clean solution.
Double check after clean that everything is deleted from debug folders.
Build it in release mode.
Build solution project to project until you isolate problematic project.
Remove COM and comment code to see if is this the source of problem.
Restart VS2010.
Restart windows.

Few moments ago I fix it with repair of .NET Framework installation (.NET Framework v4.0 Extended in my case).

I had the same issue in VS 2015. I tried the following with no success:
Close VS project and reopen
Close all open VS projects and reopen just the project that had the issue
Clean solution
Rebuild solution
Delete all files in bin\debug and bin\release
Lastly I tried Keith Robertson's answer, delete .suo (\Visual Studio 2015\Projects\[ProjectName]\.vs\[ProjectName]\v14\.suo). Although this didn't get me a good build, it did finally give me an error message stating that I had two entry points to my application. I went to application properties (Alt + Enter) and select a Startup object from the drop down.

This error seems a bit generic to me. I also went through this situation, but I managed to solve it differently than any of the ones mentioned here.
I have a project and several dependencies. And one of these dependencies has undergone a change.
When compiling the main project in debug mode, I verified that everything was ok.
However, switching to release mode and recompiling the problem occurred.Rebuild all failed and 0 Errors
By analyzing the debug output, I encountered an error:
Although the build dependencies are configured correctly. When compiling in release mode, the main project did not find the new method created in the secondary project.
So I had to recompile each secondary project one by one in release mode. After that, I recompiled the main project and everything worked.
Hope it helps someone!

I just had the same thing. For me, it helped to restart VS and run it as Administrator.

Select the appropriate target framework
- Right click on project
- Properties
- In application tab, Select the target framework

clean the solution
Try and build each project and see where the issue is.
Check each of the references (of each project) to make sure not have the yellow warning sign
Has the solution ever built?

I just had this happen to me, and realized that I left a '#error' line in my code and forgot about it. When I tried to build, the build failed but the #error line didn't show up in my errors.
Try searching all for '#error'

I fixed it on my new implementation of Visual Studio 2013 by going to the database project / Project Settings and noticing that the Target Platform was SQL Server 2014 instead of 2012 like it should be.

Once chance of getting this error is when we try re naming the service reference name, we give some other name in the service reference, but in the namespace some where it will be referring the old name, so if you delete and add a service reference then keep the same name, else we may face this error, but we can see the error in the Output window.

There are apparently many causes of this. I just found the cause of my issue: the .NET version of a new project I created was higher than the version of the top-level project. (4.5.2 vs 4.0)

I got a similar issue today, and fixed it with repair.
Start
Run…
Appwiz.cpl
(Find your installed Visual Studio version)
Right click
Change
Repair

In my case it was the wrong date and time of computer.

I was getting no feedback/messages/errors. Just that all projects failed to build.
I closed and tried again--I noticed an error saying "you are not authorized to access..."
I clicked on my account, re-entered my credentials, and rebuilt the solution.
Voila! I got what I am used to seeing when I build a solution -- plenty of errors in all their glory.
Hope this helps someone.

Here's yet another reason which may sound familiar to some. I had integrated some code into my solution that wrapped a DLL. The C# code file that came with it offered a nice managed API and handled the low-level LoadLibrary stuff to access the DLL. Both had the same base name, so I had SomeName.cs and SomeName.dll. I could just drop it into any project and it would work.
This wasn't so nice after a while as I started using it in different projects. I got copies of both the DLL and the wrapper code in multiple projects. So I figured it would be better to drop the wrapper code and the DLL into a new class library project and then reference that new project from other projects.
After I had done that, I started to get this issue. The build went well up until the very last stage and then failed without error. Output showed nothing but successes.
The problem was the name of the wrapping class library project. I used the same base name (SomeName) for this. By default the assembly name would be SomeName.dll and I already had one such file (the DLL to be wrapped), thus I had a conflict with output files.
After renaming the wrapping project and its output assembly to SomeNameWrapper, the problem went away.
This may not be your exact cause but it seems likely you have some name clash or deployment issue as well. And it is not surprising the compiler won't give you an error because there is no problem in the compilation phase, the trouble starts with deployment and apparently this does not come out in an obvious way.

I had the same problem the original poster was displaying with 0 errors and Rebuild all succeeded. The Output tab showed a message that a referenced dll was built with a higher version of the .NET Framework.
Changing the .NET framework to match resolved the issue I was having with 0 Errors and Rebuild All succeeded.

The solution:
Because Prerequisites not set for debug set only for release
01-Change solution configuration ( in main screen )
set (debug to release)
set solution platform to (Any CPU)
02-Set Prerequisites for debug ( If you want to continue in debug mode )
03-set target platform version for all Projects

Some of the files included in your solution are not in the correct directories, or you have changed the name of one or more directories in your application. In the solution explorer under Setup review the list of all files and remove those that are not properly listed in the SourcePath Property.

One of my dependency in View file caused this. Check your view files for any dependencies which is not injected yet.

Cannot find resource EntityModel.rlinq embedded in assembly

I am trying to run a solution which has entity model included but I am getting weird error which someone already had in the past and can help me solve this. My colleague says that the solution is running fine on his comp and on other computers too, but on mine comp doesn't want to work for some reason. Please let me know if I am missing something, he checked too, and it looks pretty much the same.
Here is the screenshot:
Every advice is welcome.
Thanks, Laziale

It seems you do not have OpenAccess ORM installed on your machine. You can refer this article, which demonstrates how to use OpenAccess ORM without installing.
If this is not the case and you have the product installed, you need to verify whether the OpenAccess.targets file is deployed under the MSBuild folder [C:\Program Files (x86)\MSBuild] and it tries to resolve the enhancer from the correct location. Additionally the Build Action for the rlinq file should be set to OpenAccessDeploy.

if telerik 2015 q1 is used, this issue comes. first check whether openaccess.target.dll is present in the path c:/program files(86)/msbuild. if not, place the one. then install telerik q1 installer. I got the installer from my team mate as it is not available in telerik site(deprecated)
.

I had the same issue this Offical Telerik post helped me.
TLDR:
In Solution Explorer right-click the project containing the rlinq and select Unload Project.
Right-click on the unloaded project and select Edit ProjectName.csproj (vbproj).
Add this to the end of your file:
<Import Condition="Exists('$(MSBuildExtensionsPath)\OpenAccess.targets')" Project="$(MSBuildExtensionsPath)\OpenAccess.targets" />

the source file is different from when the module was built

This is driving me crazy.
I have a rather large project that I am trying to modify. I noticed earlier that when I typed DbCommand, visual studio did not do any syntax highlighting on it, and I am using using System.Data.Common.
Even though nothing was highlighted, the project seemed to be running fine in my browser. So I decided to run the debugger to see if things were really working as they should be.
Every time the class that didn't do the highlighting is called I get the "the source file is different from when the module was built" message.
I cleaned the solution and rebuilt it several times, deleted tmp files, followed all the directions here Getting "The source file is different from when the module was built.", restarted the web server and still it tells me the source files are different when they clearly are not.
I cannot test any of the code I have written today because of this.
How can the source be different than the binary when I just complied
it?
Is there any way to knock some sense into visual studio, or am
I just missing something?

I got this issue running a console app where the source that was different was the source that had the entry-point (static void Main). Deleting the bin and obj directories and doing a full rebuild seemed to correct this, but every time I made a code change, it would go out-of-date again.
The reason I found for this was:
I had checked "Only build startup projects and dependencies on Run" (Tools -> Options -> Projects and Solutions -> Build and Run)
In Configuration Manager, my start-up project didn't have "Build" checked
(For #2 -> accessible via the toolbar under the 'Debug/Release' drop down list.)

I was just having this same problem, my projects were all in the same solution so they were using Project to Project references, so as one changed the others should have been updated. However it was not the case, I tried to build, rebuild, close VS2010, pulled a new copy from our source control. None of this worked, what I finally ended up trying was right clicking on the project and rebuilding each project individually. That updated the .dlls and .pdb files so I could debug through.
The issue here is that your dll and or your pdb files are not in sync.

Follow these steps
Just delete the bin directory from the project where the DLL is generated.
Re-build the project.
Remove reference from the project that make reference to the DLL.
Include again the reference.
Enjoy.

In addition to these answers I had the same issue while replacing new DLLs with old ones because of the wrong path. If you are still getting this error you may not refer the wrong path for the DLLs. Go to IIS manager and click the website which uses your DLLs. On the right window click Advanced Settings and go to path of the Physical Path folder on File Explorer and be sure that you are using this folder to replace your DLLs.

Some things for you to check:
Have you double checked your project references?
Do you have a Visual Studio started web server still running? Check the system tray and look for a page with a cog icon (you may have more than one):
(source: msdn.com)
Right click and close/exit it. You may have more than one. Can you debug your changes now?
Are you running the debug version but have only built the release version (or vice versa)?
Did the compile actually succeed? I know I've clicked through the "there were errors, do you want to continue anyway?" message a couple of times without realising.

With web services, the problem can be caused by using the Visual Studio "View in Browser" command. This places the service's DLL and PDB files in the bin and obj folders. When stepping into the web service from a client, somehow Visual Studio uses the PDB in the bin (or obj) folder, but it uses the DLL in the project's output build folder. There are a couple workarounds:
Try deleting the DLL and PDB files in the web service bin and obj files.
Try clicking "View in Browser" in Visual Studio.
If you previously got the source file mismatch error, Visual Studio might have added the filename to a black list. Check your solution properties. Choose "Common Properties -> Debug Source Files" on the left side of the dialog box. If your web service source files appear in the field "Do not look for these source files", delete them.

Unload the project that has the file that is causing the error.
Reload the project.
Fixed

I just had this issue.
I tried all the above, but only this worked:
delete the .pdb file for the solution.
delete the offending .obj files (for the file being reported out of sync)
build the solution.
This fixed the issue for all builds moving forward for me.

In Visual Studio 2017 deleting the hidden .vs folder in the resolved this issue for me.

This is how I fixed the problem in Visual Studio 2010:
1) Change the 'Solutions Configurations' option from "Debug" to "Release"
2) Start debugging
3) Stop debugging and switch the 'Solutions Configurations' option back to "Debug"
This worked for me. Step 3 is optional - it was working fine when I changed it to "Release" but I wanted to change it back.

My solution:
I had included an existing project from a different solution in a new solution file.
I did not notice that when the existing project was rebuilt, it was putting the final output into the NEW solution's output directory. I had a linker path defined to look into the OLD solution's output directory.
Switching my project to search in the new solution's output directory fixed this issue for me.

I had this problem, and it turns out I was running my console application as a windows application. Switching the output type back to console fixed the issue.

I had the same problem. To fix it I used the "Release Mode" to debug in VS2013. Which is sufficient for me, because I'm working in a node js\c++ addon.

My problem was that I had two projects in my solution. The second one was a test project used to call the first one. I had picked the path to the references from the bin folder's release folder.
So whenever I made a change to the first project's code and rebuilt it, it would update the dlls in the debug folder but the calling project was pointing to the release folder, giving me the error, "the source file is different from when the module was built."
Once I deleted the reference to the main project's dll in the release folder and set it to the dll in the debug folder, the issue went away.

In my case, the #Eliott's answer doesn't work.
To solve this problem I had Exclude/Include From Project my deficient file, andalso Clean and Rebuild the solution.
After these actions, my file with my last modifications and the debugger are restored.
I hope this help.

solution:-
the problem is:-
if your some projects in a solution , refer to some other projects,
then sometimes the dll of some projects, will not update automatically, whenever you build the solution,
some projects will have previous build dlls, not latest dlls
you have to go manually and copy the dll of latest build project into referenced project

I was using Visual Studio 2013 and I had an existing project under source control.
I had downloaded a fresh copy from source control to a new directory.
After making changes to the fresh copy, when building I received the error in question.
My solution:
1) Open Documents\IISExpress\config\applicationhost.config
2) Update virtualDirectory node with directory to the fresh copy and save.

My problem was that I had a webservice in the project and I changed the build path.
Restoring the default build path solved my issue.

I had this same problem and I followed the majority of the guidance in the other answers posted here, nothing seemed to work for me.
I eventually opened IIS and recycled the application pool for my web application. I have IIS version 8.5.9600, I right-clicked my web application, then: Deploy > Recycle > Recycle application pool > OK.
That seems to have fixed it, breakpoints now being hit as expected. I think that doing this along with deleting the bin and obj folders helped my situation.
Good luck!

I know this is an old question but I just had the same problem and wanted to post here in case it helps someone else. I got a new computer and the IT dept merged my old computer with the new one. When I set up TFS, I mapped a different local path than what I was previously using, to an additional internal drive. The old path still existed from the merged data on my hard drive so I could still build and run. My IIS paths were also pointing to the old directory. Once I updated IIS to the correct path, I was able to debug just fine. I also deleted the old directory for good measure.

I also experienced that. I just open the obj folder on the project and then open the debug folder delete the .pdb file and that's all.

This error also happens if you try to make changes to a source file that is not part of the project.
I was debugging a method from a .dll of another one of my projects, where Visual Studio had quite helpfully loaded the source because the .dll had been built on the same machine and it knew the path to the source. Obviously, changing such a file isn't going to do anything unless you rebuild the referenced project.

Delete all breakpoints.
Rebuild.
Done

At Visual Studio 2015, using C++, what fixed for me the the source file is different from when the module was built problem was
restart Visual Studio.

Check if the location you pointed to using mex() in Matlab is correct (contains lib and obj files which are modified to the last date you compiled the library in Visual studio).
If this is not the case:
Make sure you are compiling Visual studio in a mode that saves .lib files :
properties -> Config properties -> General -> Config type -> static library
properties -> Config properties -> General -> Target extension=.lib (instead of exe)
Make sure the output and intermediate directories match the Matlab directory in
properties -> Config properties -> General -> Output directory
properties -> Config properties -> General -> Intermediate directory

I get this issue when debugging sometimes w/ Visual Studio but when the application is served by IIS. (we have to develop in this form for some complicated reasons that have to do with how the original developer setup this project.)
When I change the file and rebuild, that fixes it a lot of the time. I know that sounds silly, but I was just trying to debug some code to see why it's doing something weird when I haven't changed it in a while, and I tried a dozen things from this page, but it was fixed just by changing the file..

In my case, the problem was that the debugger exe path was pointing to a net5.0 bin folder. I am using net6.0, so I should've updated the exe path back when I updated the target framework. Works fine now.

Debug-> start without debugging.
This option worked for me. Hope this helps!