Develop Reference

Visual Studio 2015 diagnostic tools no longer working

I have Visual Studio 2015 Community Edition Update 3 running on Windows 7 SP1 64 bit, which I use to develop C# applications.
I love the diagnostic tools during debugging to spot performance problems early on. However, they stopped working for me sometime in the last month or so (possibly related to installing Update 3, although I have no information to back that up). I see the error message "CPU Profiling while debugging is not available on this version of Windows. To see CPU usage details, run the CPU Usage tool without the debugger (Debug -> Performance Profiler...)."
Things I have tried without success:
Completely uninstalling and reinstalling VS.
Performing a repair on my VS installation
Ensuring "Use {Managed,Native} compatability mode" is disabled in debug options.
Enabling the Diagnostics Hub logging info as described in this question. No error messages that I can see appear in the logs.
This still happens even if I create a new WPF project, so I don't believe it has any project-specific cause.
Are there any other things I can try? Obviously they were working before, so I don't believe the error message about my version of Windows being unsupported.

Deleting my solution's .suo (solution options) file fixed the issue. My initial statement of this bug affecting even new projects seems to be wrong. Although, I did do a complete reinstall of VS after doing that test, so it's possible that impacted the outcome.

Full disclosure: I work at Microsoft, specifically on the Diagnostic Tools team.
There are parts of the Diagnostic Tools that won't work on Windows 7, specifically taking a CPU profiling trace while debugging. This is a limitation of the operating system and ETW. If you are just interested in the graphs and debugging events, those should work. You can turn on logging for our tools which might give you some insight into why they are not working:
HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\14.0\DiagnosticsHub\LogLevel
HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\14.0\DiagnosticsHub\LogDirectory
For LogLevel you can use one of the following strings "All", "Info", "Debug", "Warning", "Error" (In your case I would use All to better see what is happening). As for LogDirectory it is a directory of your choice "C:\Logs". When your done reproing the scenario, close VS to flush the logs and don't forget to delete these keys as the diagnostic tools logging is pretty system intensive.
You should be able to search for "Error ---" in the logs to get an idea of what is happening. We have seen problems with certain VS extensions and custom projects.
Also, feel free to also post the issue at: https://connect.microsoft.com/ Each issue that is received there gets turned into a bug and assigned to the corresponding team.

I had som issues with that a while ago.
1) Check Tools>Options>Debugging>General>Enable Diagnostic Tools while debugging
2) Check Tools>Options>Intellitrace>Enable intellitrace

I had the same issue, although deleting the .suo file did not help, I also repaired Visual Studio 2015 Professional and then it worked. So for future readers, if deleting the .suo does not help, try to also repair Visual Studio and vice versa.

None of the others worked for me. What I had to do was close all Visual Studios and re-opened it and the diagnostic tool worked.
(I deleted the .suo file, made sure all the correct options were enabled, but because I had another Visual Studios session running, none of it worked until I closed all)

I had already another visual studio instance running with diagnostic one. That was the issue for me.

I faced this problem today and it was not easy to find working solution.
This helped to me:
Reinstall Cumulative Servicing Release for Microsoft Visual Studio 2015 Update 3 (KB3165756)
Direct link to download: http://go.microsoft.com/fwlink/?linkid=816878.
After Repair action (I had it installed before, otherwise install) prompted to restart computer, did it and Diagnostic tools worked again.

I had a similar problem with Visual Studio 2015 Pro Update 3 running on Windows 10 Home. The runtime display of memory and cpu usage stopped working. Deleting the .suo file fixed the problem, as indicated by proc-self-map's answer. The .suo file was buried in the .vs hidden directory so I removed the whole .vs subdirectory. Now the runtime display of memory and cpu usage works like a charm again. No reinstall required.

VS 2015 High CPU Usage on File Save

With Visual Studio 2015 I have noticed that if I have multiple solutions open with a common project to all solutions, if I so much as edit and save one .cs file belonging to the common project, all Visual Studio 2015 instances will consume CPU for 10-15 seconds. Note that the common project is fairly large.
I don't recall this happening with Visual Studio 2013. It is common in my workflow to have 8-9 instances of Visual Studio open all with solutions referencing the common project, so I feel as though I would have noticed this behavior with Visual Studio 2013 (my development machine has 32 GB of RAM which makes this type of workflow possible).
I have tried:
Disabling CodeLens
Uninstalling ReSharper
Disabling the four C# Intellisense features found in Tools->Options
Temporarily Disabling Static Code Analysis Solution Wide (for all loaded solutions)
I also launched a separate instance of Visual Studio 2015, enabled Microsoft Symbol Servers and profiled (via Debug-> Profiler-> Performance Explorer -> Attach/Detach) an offending Visual Studio instance while it was consuming High CPU.
This image shows the profiler summary and you can see from the graph high CPU usage between ~12s and ~27s.
84.46% of the samples were in Thread::intermediateThreadProc, and the majority were exclusive samples, but of the inclusive samples, it appears as though it was doing some sort of code analysis.
With this information I assume that some sort of background code analysis is being performed with all Visual Studio 2015 instances (including those in the background). Does anyone know how to disable this? Or if my assumption is incorrect, any other suggestions?
Update 9/12/2015
Interestingly, if I perform the same profiling with ReSharper 9.2 installed, I get a similar result, but with JetBrains.Platform.Satellite.exe at the root of the "Hot Path" (instead of devenv.exe).
Update 10/11/2015
I believe this is the issue:
How to disable real time compilation in Visual Studio 2015
Is there a way to disable real time compilation on save? Or at least have it not be so intrusive? The operation most likely to follow "Save" is "Build", and because all of the visual studio instances are recompiling their respective solutions (without being asked), the "Build" operation in the active solution is severely hindered.

Found here (http://www.itgo.me/a/x8021838007883560399/how-to-disable-real-time-compilation-in-visual-studio-2015) :
"go to tools, options, text editor, C#, Advanced and uncheck Enable full solution analysis. This should stop your problem as the solution won't be checked every time unless you build it."

ReSharper "Cannot resolve symbol" even when project builds

My Tools:
Visual Studio 2012 Ultimate + Update 1
ReSharper v7.1.25.234
My Solution Build Status: Build Successfully
But when I install ReSharper and ReSharper code analysis is enable, many keywords of my code are red with this error:
"Cannot resolve symbol XXX"
Another picture of my project >>
The ReSharper “CANNOT RESOLVE SYMBOL” errors are everywhere, but my project build process is successfully, and it works correctly.
Additional Note: If I disable ReSharper Code Analysis, my project will be Normal, but I want to use ReSharper code analysis.
I tried ReSharper → Options → General → Clear Cache. But I still have this problem!
One month ago, I got these errors when I uninstalled Visual Studio 2012 RC and installed VS 2012 RTM.
I've already uninstalled and installed ReSharper again. But I have this problem yet!
My solution has five projects >> two loaded projects (main project + resource project) and three unloaded projects
I realize that my Visual Studio also has bigger problems (More information on Stack Overflow)
I can't add any reference to my projects (even inside new solutions and new projects)
I can't install any package (by "Packet Manager Console" or Manage NuGet Package)
I can't update any package (by "Packet Manager Console" or Manage NuGet Package)
I've done a lot of suggestions (of myself and others)
Re-resister some DLL files
Using some windows and registry repair tools
Remove ReSharper
Repair Visual Studio
and...
But I could not solve it.
I'm thinking of installing a new Windows :(
What is wrong, and how can I fix it?

Try Visual Studio → menu Tools → Options → ReSharper, Suspend button and Resume again (no need to close the window). This works in my case.

VS -> Tools -> Options -> ReSharper Suspend button
Clear Contents of -> AppData\Local\JetBrains\ReSharper\v7.1\SolutionCaches
VS -> Tools -> Options -> ReSharper Resume button

This worked for me (VS2012u4, R# 7.1.3):
Resharper > Options > Environment: General > Clear Caches
Restart Visual Studio

Clear Resharper cache: Resharper -> Options -> General -> Clear Caches, close and reopen the solution. It worked in R# 9.0 Update 1

This happens in ReSharper when you have two different versions of the same library in your solution. For example project A references automapper version 1.1 and project B references automapper version 1.0.
Visual Studio will often compile and run as expected in the situation as it chooses one of the DLLs to bind to. However ReSharper gets massively confused. For me this should be a ReSharper error that it asks you to resolve rather than just going bonkers.
UPDATE:
I ran into this two days ago (a day after I made this post) by total coincidence and came across this link where they say that it is caused by a bug in the VS API. I tried everything that they recommended and was unable to resolve it even temporarily: I had Autofac 2.6.x that I'd downloaded from google.code and then swapped it over for the NuGet package version and it willfully refused to see the new reference no matter what I did.
They suggest installing the R# 8 EAP but for me it was less hassle to just downgrade to the old version of Autofac.
Not much in the way of help, but maybe useful.

This was happening to me with Visual Studio 2015 and ReSharper Ultimate 10.0.2. I tried pretty much all the solutions written prior to this answer (apart from any reinstallations) and nothing worked.
I got it working again with a variety of the above steps in a very specific order:
ReSharper → Options → Environment → General → Clear Caches
this must be done before suspending ReSharper as otherwise this option is unavailable
this clears out the files in C:\Users\YourUsername\AppData\Local\JetBrains\Transient\ReSharperPlatformVs14\v04 as mentioned in some other posts
Tools → Options → ReSharper Ultimate → Suspend
Close Visual Studio
this actually performs the ReSharper cache clear
Open Visual Studio
Open the solution
I waited for Visual Studio to detect there were no code issues in IntelliSense and may have performed a build at this point.
Tools → Options → ReSharper Ultimate → Resume
Hopefully after the last step you can breathe a sigh of relief that you don't have to reinstall anything, I certainly did!

It's usually happen by config file corrupt or wrong detect.
Just delete .vs folder, restart VS to reset config. It will work almost case

I had similar problems and cleared the caches found at:
AppData\Local\JetBrains\ReSharper\v7.1\SolutionCaches
Solved the problems for me
Running VS2012 u3

I had the same problem (VS 2017). In my case it was different versions of target framework - one assembly targeted 4.52, another 4.62 - after setting those to the same version in both assemblies it started working again.

As you see, the solution is what everyone has already mentioned - simply by Suspending ReSharper, then Clearing the Caches, and finally Resuming it. But, no one mentioned how to do it without closing/restarting Visual Studio.
Just follow these steps:
Getting ReSharper Cache Location
Manually by going to ReSharper Options > Environment > General > Store Solution Caches in (Combo Box) (marked 2 in the image). Selecting Custom Folder, then Copying the location of the Caches Folder from the text box shown (marked 3 in the image). Reverting the settings back. The 1 marked shows the ClearCache Button. It's usually wouldn't work so leave it.
Suspending ReSharper
You can do this by going to Tools > Options > ReSharper Or ReSharper Ultimate > Suspend Now (Button)
Clearing the Cache
Go to the location copied earlier in step 1 and delete everything in that folder. And yes, I do mean everything.
Resuming ReSharper
You can do this by again going to Tools > Options > ReSharper Or ReSharper Ultimate > Resume (Button)

Above links of clearing the cache and/or suspending the ReSharper did not work for me. I just 'refreshed' the project, which was showing this problem, from the solution explorer and the problem goes away. Sadly, it keeps on recurring and only option it to keep on refreshing every time this problem recurs.
I have VS2012 with ReSharper 8.1 on Windows 8

I was just having the same issue with ReSharper 8.2 in Visual Studio 2013, and none of the usual solutions here of clearing caches, suspending ReSharper or re-installing ReSharper was working.
In my case I ended up solving it as follows... I looked at one of the symbols that it couldn't resolve and noted it was in System.Web.Http.dll. I then found that this was in the Microsoft.AspNet.WebApi.Core NuGet package. I used the package manager console to try and uninstall that package, except of course it told me that it couldn't due to other dependencies.
So I uninstalled each dependency up to and including Microsoft.AspNet.WebApi.Core, and then re-installed each package again in the reverse order. ReSharper picked everything up correctly as it was installed, and now seems fine.

I had the same issue and unloading and reloading problematic project helped me to clear out this issue for ReSharper. Hope this helps.

I ended up needing to request Resharper to clear its cache along with doing it manually through Windows File Explorer. This finally resolved the issue for me.
(As reported in many of the solutions here) RESHARPER > Options... > Environment > General > Clear Caches.
Close Visual Studio.
Go to this path in File Explorer for Resharper 10 in Visual Studio 2015: %localappdata%\JetBrains\Transient\ReSharperPlatformVs14
Delete all subfolders and their contents within that folder.
Restart Visual Studio, reload your Solution and wait for Resharper to initialize itself for the Solution.

For me for VS2015, I had to update Resharper to version 2016.2.2 to resolve the issue.
I had already tried (of which none worked for me):
suspending / resuming
suspending / clearing cach (using tools > options button) / resuming
suspending / clearing cach (using Windows file system) / resuming
moving cache to solution folder / restarting visual studio
many other combinations of all or some of above
I hope that may help someone.

Resharper -> Options
Caches -> Store solution caches in: (Change folder to another one).
Or try to manually clean up R# cache folder

I'm using 7.1, and this worked for me:
Uninstall resharper
go to %appdata% and remove JetBrains\Resharper and ..\Local\JetBrains\Resharper folders
re-install resharper

None of the cache cleanup worked for me. All of the symbols in any of our private NuGet repros just stopped being picked up with R# enabled, very frustrating.
I got this feedback from JetBrains support, which DID work, after toggling and restarting VS2019:
disable the following option - ReSharper | Options | Environment | General | Read solution model directly

I did everything above with no fix.
Then I did a step from another SO Q/A (don't remember which one) which was to set System.Web.Mvc to Copy Local true. Recompile my project and the errors went away.
When I set this assembly back to Copy Local false, the errors didn't return.

I my case, I tried all the suggestions above.
But, at some point I realized that the problem persists even if Resharper is suspended.
So, I looked for similar problem in VS itself and found the solution in the comments for the accepted answer in this SO post.
I'm listing my steps for brevity.
VS -> Tools -> Options -> ReSharper Suspend button
Build solution. Notice all references still unresolved
Clean the solution
Restart VS
Build the solution without Resharper. Notice all references resolved
VS -> Tools -> Options -> ReSharper Resume button

I am using VS2015, R#10. None of the suggested solution worked for me. I deleted the contents of the bin folder of my solution and rebuild the entire solution, that seems to have resolved the issue. Before deleting the contents of the bin folder, I had tried suspending and resuming R#, doing clear cache from R# -> option -> general setting, and also manually deleting the contents from \AppData\Local\JetBrains\Transient\ReSharperPlatformVs12\v01\SolutionCaches.. Hope it helps someone.

I was having the same issue in my Visual Studio 2015 with Resharper Ultimate and tried the solutions as suggested above, but none worked for me.
Then upgrading Resharper to latest release solved my issue.

What helped in my case after several of the suggestions above didn't:
Removed one project reference (of one of the libraries where ReSharper claimed not to be able to find it even though it was correctly referenced).
Use ReSharper’s "Resolve" on one of its usages to add the reference again.
After that, it worked fine, even though none of the project files were actually modified in the process.

I have the same problem.Clean Resharper cache and Suspend Resharper not worked for me.I just close visual studio, uninstall Resharper,and then install Resharper,the problem was gone.

I was referencing a NetStandard2.0 project that didn't get recognized by R#.
I cleared the caches but that did not help me.
Downloading the latest version and updating R# did work for me.
This is the version I'm now running:
JetBrains ReSharper Ultimate 2017.3.2 Build 111.0.20180201.63358
ReSharper 2017.3.20180201.111630
Just download R# and it will recognize already installed versions. Updating to the latest version is really easy.

When I disabled ReSharper, Visual Studio was also giving the same error, even though the project built successfully. What I did to resolve the issue was:
Remove the project from the solution.
Right-click the solution, Add Existing Project, select the project file and add it again.
After performing these steps, the syntax errors went away in Visual Studio, and after I enabled ReSharper again, it also had no errors.

I also had this problem. All previous solutions did not help for me or helped for a very short time.
In my case, the problem was that I connected the .Net Framework 4.7.2 project to a project that has version 4.5.2. After I updated both projects to version 4.7.2, the problem was resolved.
I think that to solve the problem you need to have the same version of the projects. Or connect a smaller version to a larger one, but not vice versa, as was the case in my case.

In Rider 2020.3 I just did a Build -> Clean, and then it worked.

For me, I think my solution just got caught in a weird state when I was changing which branch of my local Git repo I was on. Simply switching to the previous branch I was on before the problem started, telling VS to reload all the files, then switching back to the desired branch and reloading again fixed it.

We saw this problem as well, specific to files which were shared by multiple projects. There is a combo box in the upper left corner of the editor window that lets you switch project context for the file (and hence the references that impact symbol resolution).
Resharper makes it easy to accidentally open the wrong "version" of a shared file by its "go to file or symbol" commands.
Switching context back to the project I use in the solution was all I needed to do to fix this issue.

How can I choose between 32-bit or 64-bit build in C# Express?

I'm having a problem when I try to build my solution in C# Express 2008. I need to build it for 32-bit architecture, but it always build for 64-bit.
In Visual Studio 2008 I can choose the architecture, but I can't find this option in C# Express.
Is there a way to do this in C# Express?

Have a look at what the differences look like in the project file in the full Visual Studio, and hand-craft the same edits to your C# Express project - VS will respect those changes, even if it won't let you make them from within the IDE.
EDIT: As Jeff points out in the comments, if you go to Tools -> Options, tick the "Show all settings" box at the bottom left. Then under "Projects and solutions" tick "Show advanced build configurations". That will let you edit a lot more build options, including the target architecture. You may need to go through the Configuration Manager and create a "New Project Platform" however.
Even when you've done this, bear the first paragraph in mind for other options which simply aren't available within C# Express: it's still using the same build engine (msbuild) underneath, so as long as it isn't using any tooling specific to more powerful versions (e.g. the static checker for Code Contracts, only available for Premium and Ultimate) you should be fine.

Look at this question:
How to switch between debug and release in Visual C# 2010 Express?
Following same approch suggested there, you will be able to set architecture for your program in Express editions. The problem it's that,by default some "advanced" options are disabled in Express editions, but you can easyly re-eanble them.

I found it.
"Tools > Options > Project and Solutions > General > Show advanced build configurations"
Thank you all.

By default, C# Express hides solution configurations from you. However, you can change this in the Tools->Options dialog so that you can then specify new build configurations and change their platform targets.

In the project properties, you should be able to select the "Platform Target" - this can be "Any CPU", "x86", "x64", or "Itanium" for me (in VS2008). Is this selection not available in C# Express?

I was getting this error as well, since I was running a 32-bit application on a 64-bit machine. I fixed this by going to the IIS app pool and changed the support 32bit option to true.

My project in Visual Studio is Read Only. What did I do?

I must have done something wrong. I have a C# project in Visual Studio 2008. All of a sudden I see a lock on my classes and when I hover the class names on the top tab I see the class name as : C:\Myprojects\Oder.cs[Read Only] !
Has something weird like that happened to you before?

In my case it was a ReSharper 9.0/9.1 related issue. After clearing the ReSharper cache, I was able to edit files in my solution again.
Clearing the ReSharper cache can be done here: ReSharper -> Options -> Environment -> General and click: Clear Caches and restart your visual studio.
(The image is contained within the first of the linked JetBrains articles).
JetBrains instructions:
Ultimate Guide to Speeding Up ReSharper (and Visual Studio) - Performance degradation after ReSharper upgrade
ReSharper Online Documentation

A couple of possibilities spring to mind:
Have you added the project to source control?
Have you marked the project folder (and all it's sub folders) as read only?
Of course, someone else may have done either of these things if they have had access to your machine.

One Possible stupid thing.
Your project is still running and you forgot that. Stop debugging (CTRL + F5)
How do I know. Guess..

Restarting my computer worked for me. My project became read only in between compiles - suddenly I couldn't save changes to files, Visual Studio started presenting me with 'save as' dialog boxes, and SVN couldn't commit or clean the project because "sqlite could not write to readonly database." Checking the file properties on the files in Windows Explorer showed that none of them were marked read-only. I was able to make a backup copy of the project, then I restarted and it was fine.

Restart your Visual Studio and add the project again. Worked for me.

Close, then reopen the file.
Still a pain, but at least it's less costly than completely closing visual studio.

You can try: file -> Source Control -> Go online

IDE-integrated source control?

Sounds like your source files are or have been under source control. Many source control systems will set files to read-only when they haven't been checked out for editing.
Total Commander makes it really easy to change file attributes recursively, but most likely Windows can also do this :)

Much in line with what Morten Mertner said, (if you by chance are using TFS Source Control like I am) I did a manual checkout of the file and it resolved the issue for me.

For me the problem is that the files are locked while the application is running.
In this state, Visual Studio 2013 displays the lock icon in the file tab and when you try to edit the file, a dialog box with this message appears:
Changes are not allowed for this module as it was not built for changes while debugging or the target .NET runtime version does not support it.
In Visual Studio 2015 as well, the lock icon appears in the file tab when the application is running. but the dialog box and message are not displayed.
Stopping the application causes the file to become unlocked.