Develop Reference

Use .net DLL with broken References

I have to use a DLL as an API in my application (C#, .NET 4.5). I can reference the DLL normaly. No error at all. But if I want to use any class of this DLL, I get the following compile error:
Error CS1705 Assembly 'Assembly_X' with identity 'Assembly_X,
Version=12.3.0.0, Culture=neutral, PublicKeyToken=c878e80841e75d00'
uses 'Assembly_YY, Version=65535.65535.65535.65535, Culture=neutral,
PublicKeyToken=c878e80841e75d00' which has a higher version than
referenced assembly 'Assembly_YY' with identity 'Assembly_YY,
Version=12.3.0.0, Culture=neutral, PublicKeyToken=c878e80841e75d00'
Then i checked the DLL (Assembly_X) in ILSpy. The Assembly_X has two references to Assembly_YY: One with the version 12.3.0.0 and one with the version 65535.65535.65535.65535.
I tried the "bindingRedirect" in the App.config. But since the error occures during compile time this doesn't help.
I don't have the source code of Assembly_X or Assembly_YY.
How can I use this DLL or repair it?
UPDATE
The developers of the dll finally answered my call for help. The only work around they know of is to use Visual Studio 2013 instead of Visual Studio 2015 or 2017. It seems VS 2013 is not bothered by these double reference at all.
They write, that the error is created by a encrypting tool for the dll.
Thank you all for your ideas and help.

It looks like the first DLL is referencing a library which is a higher version than the other DLL you are using.
so you have 3 DLL's to consider: A, B & Bv2
Your project is referencing A & B
But A references Bv2 (an updated version of B)
SO when you go to use functions of A it throws an error because it finds B instead of Bv2.

The problem basically that you are referencing 'Assembly_X' which references assemblies 'Assembly_YY' versions 12.3.0.0 and 65535.65535.65535.65535 and you referenced only 'Assembly_YY' version 12.3.0.0 in your application and didn't reference 65535.65535.65535.65535
Now according to the problem explanation on Microsoft Docs, and your example which you don't have the source code for the assemblies you have to:
Add a reference to 'Assembly_YY' version 65535.65535.65535.65535 of the DLL to your application to make it compile and to enable the application to run, you can provide an application configuration file that includes a <dependentAssembly> element that uses <assemblyIdentity> and <codeBase> child elements to specify the location of version 12.3.0.0 of the DLL.

You are referencing a higher version of DLL then the one you currently have.
You will need to add the reference to the higher version assembly:
'Assembly_YY, Version=65535.65535.65535.65535, Culture=neutral, PublicKeyToken=c878e80841e75d00'
in order to solve this.
Right now you are referencing
'Assembly_X' with identity 'Assembly_X, Version=12.3.0.0, Culture=neutral, PublicKeyToken=c878e80841e75d0
If this is a downloadable library, search for it in the nuget package manager and download it.
If it's a library written by you, obtain the latest version of the library and add it to your project.

Where is the System.Net.Http.WebRequestHandler source code?

To much fanfare it was announced that there was now a Roslyn powered index for the .NET Reference Source and that
The version of the framework that we currently have indexed is .NET framework
version 4.5.1.
Yet when I go there to look at HttpClient code all I get are stubs and I cannot find any code for the bits that make it run like System.Net.Http.WebRequestHandler.
Where can I find this code and why hasn't it been included already?

I found the solution on blogs.msdn.com:
"The WebRequestHandler is not included in the System.Net.Http DLL but rather in System.Net.Http.WebRequest DLL so you have to explicitly include that as a reference in order to see it."

add assembly System.Net.Http.WebRequest

Assembly binding error when building Office add-in: "FindRibbons" task failed unexpectedly

We're trying to set up a Jenkins (build server) job to build our Office add-in based on VSTO. However, I keep getting a strange error that fails the build process after the DLL is copied to the bin directory of the project:
Error 11 The "FindRibbons" task failed unexpectedly.
System.IO.FileNotFoundException:
Could not load file or assembly 'MyAddIn, Version=1.0.0.0, Culture=neutral,
PublicKeyToken=null' or one of its dependencies.
The system cannot find the file specified.
File name: 'MyAddIn, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'
So the problem is that the "FindRibbons" task, triggered by the Office add-in build target, has successfully identified the MyAddIn DLL as being an Office Add-In, but is not able to locate and load it!
Any ideas? I'd love to be able to debug the FindRibbons task directly but hooking into and debugging the compile process seems a little extreme...
Here are some observations:
In our build server's Fusion logs for binding the MyAddIn assembly it looks like it's looking in the folder where MSBuild.exe lives (C:\Windows\Microsoft.NET\Framework\v4.0.30319\) and nowhere else.
On my dev machine, there is no Fusion log entry for MyAddIn! But the build process succeeds and Kivo works fine.
On both my dev and build machines I also have Fusion log entries for WhereRefBind!Host=(LocalMachine)!FileName=(PresentationCore.dll) and ExplicitBind!FileName=(MyAddIn.dll) which show the binding succeeding.
This error comes up on the build server whether I use Visual Studio or MSBuild from the command line to build the project.
I've ensured that the .NET/MSBuild/VS2012 versions are identical on both my dev machine and the build server and the error still occurs. The only difference seems to be that the build server is running Windows Server 2012 (since it's Azure, and we can't spin up a Windows 7 image).

This has worked for me every time I upgrade Visual Studio - I don't use ribbons.
This worked for my solution, but use at your own risk:
Open the following file in an XML editor (make a backup first): C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v10.0\OfficeTools\Microsoft.VisualStudio.Tools.Office.targets (the v10.0 part may be different for you, e.g., it might be v14.0)
Remove the following section:
<FindRibbons AssemblyName="$(AbsolutePathToCustomization)" TargetFramework="$(TargetFrameworkVersion)">
<Output TaskParameter="RibbonTypes" ItemName="RibbonTypesCollection"/>
</FindRibbons>
Replace all occurrences of "#(RibbonTypesCollection)" with the empty string ""
Save the file and restart the visual studio

If you migrated the project from a previous version of Visual Studio, be sure to remove the ExcelLocale1033 and SecurityTransparent attributes from the AssemblyInfo.cs file (as answered by Swati in this other question)
If the project still fails to build, it may be because your .csproj file has some references to msbuild's tasks of previous versions of Visual Studio. I suggest you to create a new empty Excel AddIn project, and uses the msbuild structure of the new project file as base for your project.

I had this problem. It was apparently caused because I changed the "Copy Local" setting on reference "Microsoft.Office.Tools.Common.v4.0.Utilities" from True to False. ISYN. (I sh*t you not)
I had upgraded a project from VS2012 to VS2013 and noticed that that reference was the only one set to "Copy Local = True". So I set it to false, because it was different. This caused the error. Changing it back to True solved it.

I had the same error message and finally found a fix. The problem stemmed from the VSTO project being targeted for .NET 4.0 (it seems this is the minimum for VSTO4), while also referencing an assembly built for .NET 3.5. The real culprit was that I had a class in the VSTO project deriving from an interface defined in the .NET 3.5 assembly that in turn derived from a .NET 3.5 library interface. i.e.,
using System.Xml;
class MyVSTOClass : IMy35AssembyInterface // This caused the error
class MyVSTOClass : IXmlSerializable // This compiled OK
using System.Xml;
interface IMy35AssembyInterface : IXmlSerializable
The fix was to update the .csproj to explicitly reference the older version of System.Xml.dll and System.Data.dll which would otherwise default to 4.0 and conflict with the 3.5 assembly references.
<Reference Include="System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089, processorArchitecture=MSIL">
      <!--<Aliases>Data2</Aliases>-->
      <HintPath>C:\Windows\Microsoft.NET\Framework\v2.0.50727\System.Data.dll</HintPath>
      <SpecificVersion>True</SpecificVersion>
      <Private>False</Private>
    </Reference>
 <Reference Include="System.XML, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089, processorArchitecture=MSIL">
      <!--<Aliases>Xml2</Aliases>-->
      <HintPath>C:\Windows\Microsoft.NET\Framework\v2.0.50727\System.Xml.dll</HintPath>
      <SpecificVersion>True</SpecificVersion>
      <Private>False</Private>
    </Reference>
For those who need to simultaneously reference both the newer and older versions of a DLL, note that it is in theory possible using:
extern alias XmlDll1
using XmlDll1::System.Xml
See http://geekswithblogs.net/narent/archive/2008/11/11/126940.aspx for more info.

This problem can also be caused by adding a reference to an unsigned assembly to a signed/strong named add-in project. In my case I added the RestSharp Nuget package and started receiving this error on build as soon as I referenced RestSharp in code. After some digging I noticed that RestSharp was the only unsigned assembly in the project references. If you have this problem, there are 3 possible solutions:
In the case of RestSharp, I found that there was a signed version available on Nuget - searched for "restsharp signed" and installing that solved the problem.
If you have access to the source code, you can configure Visual Studio to build a signed version of the assembly in the Project Properties page.
If you do not have access to the source code, you can sign the assembly with your own key by following these instructions.

I had the same error and none of the answers from the internet help me fix this problem. The reason why I was getting that error is because I was referencing an assembly of type Console Application. I changed that assembly to be of type ClassLibrary and I did not got that exception any more.
Also I would only get that exception when inheriting from a class that was located on my ConsoleApplication. It took me forever to figure it out.

May be a little late here, but I just resolved this for myself - after following numerous suggestions (via google) all of which did not solve my problem I manually went down the line. Turns out I had compiled a set of libraries with a dependent assembly with a lower version (not the latest). In my main project I also had a reference to this dependency but it was pulled via nuget and was at the latest & greatest version. For some reason VS.NET couldn't figure that out and would completely trip out and drop the error you posted. Once I updated the set of libraries to the latest version of the dependency all worked as normal.
The crazy part is - it worked fine initially and then out of nowhere the issue came about. Hope this helps someone along the way.
After enabling Fusion the output showed that it was looking for the assembly in the msbuild/ folder.

I just encountered this same situation today, futzing around for a bit, restarting VS and then rebooting my machine without any success. Than one warning popped out at me - One of my dependent assemblies was not strong named. Setting that assembly to be strong-named solved the problem.

I had the same issue, and even after reading KKG's answer I could not resolve mine.
It turned out to be much simpler for me, but not less frustrating and time consuming. I was working in a Win8.1 VM which does not ship with .net3.5 by default. My .net4 VSTO4 project was referencing an assembly that requires 3.5 somewhere. The same project compiled find on my other VM which was Server2008 and had 3.5 enabled.

In my case, the cause for this error was the mere existence of a field of a generic value type in the assembly (not kidding), e.g.:
class Foo
{
ImmutableArray<int> foo;
}
Workaround (if the additional indirection is acceptable performance-wise):
Wrap the value type in a reference type. This can be done generically with something like
public sealed class Box<T>
{
public readonly T value;
public Box(T value)
{
this.value = value;
}
}
then foo can be of type Box<ImmutableArray<int>>.

I have experienced this same issue with an add-in for Outlook.
The solution for me was to set Embed Interop Types to True on my reference to Office.dll.
This however caused the add-in to crash during startup with an Access Denied on Microsoft.Office.Interop.Outlook. I fixed that issue by setting Embed Interop Types to True on all references to Microsoft.Office.Interop.Outlook.dll as well.

This error can be caused by a clash of dependency versions. For example:
YourAddIn
-- OtherLibrary v1.3
-- BaseLibrary v1.0
-- BaseLibrary v2.0
If a newer version of BaseLibrary v2.0 is released and updated in your project, however this version introduce a breaking change in your other dependency OtherLibrary, you will see this exception because OtherLibrary is still trying to find the old methods that doesn't exist in newer assembly.
Update OtherLibrary with the latest packages will resolve this clash of dependency versions.

This can also happen if the Microsoft.Office.Tools.Outlook.v4.0.Utilities reference is set to <Private>False</Private>.
<Reference Include="Microsoft.Office.Tools.Outlook.v4.0.Utilities">
<!-- Required for FindRibbons task -->
<Private>True</Private>
</Reference>

"An assembly with the same simple name has already been imported" error without duplicate reference

I'm getting the following error:
error CS1704: An assembly with the same simple name
'Interop.xxx.dll, Version=1.0.0.0, Culture=neutral,
PublicKeyToken=null has already been imported. Try removing one of the
references or sign them to enable side-by-side.
Everything I've seen says that I am referencing two assemblies with the same name and I need to remove one of them. However, I've checked and I'm only referencing it once.
This also only happens when I'm using msbuild to build from the command line on my dev box. If I build through Visual Studio or do a clean build on our CI server I don't see this error.
I've tried completely removing all of my source and building from scratch to more closely resemble the build machine but no luck.

So it looks like I can't read today!
The project had a reference to the Interop and a COM reference that generated the "same" interop. So there were two and I just didn't search very well. I still don't understand why it worked in other places but this did fix it.

In the Error List window, the project that was triggering this error was listed in the Project column. I got around the error by doing the following:
I unloaded the listed project (right-click => Unload Project)
Opened the XML for edit (right-click the unloaded project => Edit {ProjectName.csproj}).
Searched for the offending .dll, and noticed it was listed multiple times in the XML
Removed the entire Reference tag related to the offending dll, and did so for every copy of the reference except the first one listed
The reason it was listed multiple times was because several referenced libraries used that dll. This shouldn't be a problem, in and of itself, so I'm not sure what caused this error to suddenly pop up for me. I'll update this answer if I figure that out.

In my case the duplicate entry was caused by a NuGet package reference and a direct file reference to the same assembly in the packages folder. I am not sure how the project got into this state, but unloading the project and searching the XML file for the offending assembly name resolved the issue for me.
Note that in my case this started happening after updating a NuGet package to a newer version with no other changes to the project, so this maybe caused by a bug in NuGet.

If this is a web project, are there any strong-named references to the other version there? Those won't show up as a project dependency, but will cause a run-time error like you describe. Hope that helps

I had this problem but in my case, I had an old copy placed in the current folder for the EXE loading my component, that was loaded together with the current one, that was loaded by hand from my projects folder. Deleting that old copy solved my problem.
I used Debug > Windows > Modules window to see which modules were loaded at that time and that solved my problem.

For others facing the same as me: if building via command line using property AssemblyName, it will overwrite all assemblies generated by all solution projects - in other words, you will end up with (N -1) assemblies named the same where N is the no. of projects - the startup one (which generally will generate an exe).
This happens because all build command line properties are global and overwrite any project-specific setting. See this and this.
From the msdn link mentioned above:
Global properties are properties that are set by using the
/property switch on the command line, or properties that are set by
the integrated development environment (IDE) before a project is
built. These global properties are applied to all projects that are
built by using this Engine.
In my specific case, where Jenkins is the CI tool, I ended up adding a windows batch command at the end to rename the .exe only to what I originally intended when passing the AssemblyName parameter.

For those developing UWP projects that have project references that include specifically the Microsoft.Windows.SDK.Contracts nuget package (or other dependencies that reference it), this is a common error when the version of the SDK contracts is targeting a different version of the runtime to how your project is configured.
For instance, when targeting Windows 10, version 1903:
Any dependencies or reference projects should target or at least support the same runtime version.
it is common thought process to update all NuGet packages when a new stable version is available, but this is not always a helpful practise on its own. Just because a new stable version of a package is available does not mean that you should or that you can easily use that version.
Even though this package for SDK contracts has a stable update, it is not compatible with my main project configuration, Nuget does not know this so it allows the update.
This package is specifically designed to provide windows dlls for project types that DO NOT have windows platform targeting support, it copies the same dlls that are included by the UWP targeting config. By installing later versions of the package the references from the satellite project will be included in the output along with those provided due to platform targeting, ultimately causing OPs error.
There are similar SDK and targeting packs for Windows IoT Device Runtimes, this information should help you identify and resolve those issues if you get stuck on this issue as my team often does :)

In my case, the issue was on wrong characters in the ProjectReference section of my csproj file.
Background
I have a project that references another library I maintain, which I publish as a NuGet package.
Whenever I make changes to my library, I usually reference the local dll in my project to test and make sure everything looks good before I publish the library as a NuGet package.
When testing, I just comment out the PackageReference line and uncomment the ProjectReference one so it references my local dll, like so:
<ProjectReference Include="..\..\my-class-library\MyClassLibrary.csproj" />
<!--<PackageReference="MyClassLibrary" Version="2.0.1"/>-->
Root cause
I had the slashes inverted, so I was using / rather than \ in the path, like so:
<ProjectReference Include="../../my-class-library/MyClassLibrary.csproj" />
Once corrected, the issue went away.

Try this instead: remove Interop.xx.dll from the reference section in Solution Explorer and Rebuild the project

In our case this error was shown when we had a duplicate reference inside the .csproj file (although I have no idea how this happened).
The difference to an already posted answer is that, in our case, one was a project reference and another one was direct binary reference to a dll.
Once we removed one of those, project correctly compiled.

Determine Project References to mscorlib

Hey folks, I've got an ASP.NET web site project that for some reason is insisting on referencing both mscorlib 1.0.5 and mscorlib 2.0, and I can't figure out why.
I've analyzed all the referenced DLLs using NDepend, and they all appear to only reference mscorlib 2.0. I've got a couple web references, but I can't imagine why that would create an additional reference to the 1.0 dll.
Anyone have any ideas why I'd be getting this additional reference, or what I can use to find out that information? NDepend is great, but just comes back and says "found 2 references, using the newer version", so it doesn't help me figure out why I have the extra reference...

I think at this point your best bet is to use ildasm. Using ildasm on the assembly will bring up a node named "Manifest". Double click on that node and it will dump out the IL representation of assembly references including the referenced version number. Repeat this for all of your DLL's until you find the one referencing the 1.0 version.
EDIT
Another possible solution would be to enumerate the Assembly values and there associated GetReferencedAssemblies method. This will return an array of AssemblyName values which have a corresponding Version member. This should contain the actual version of the referenced assembly vs. the one that was actually loaded.
I'm not 100% sure on this matter and don't have a convenient way to test it right now.

Try removing the reference and recompiling - that will tell you what (if anything) depends on the older version.

An errant reference may be residing in your web.config file.