Warning: Found conflicts between different versions of the same dependent assembly

This warning means that two projects reference the same assembly (e.g. System.Windows.Forms) but the two projects require different versions. You have a few options:

1. Recompile all projects to use the same versions (e.g. move all to .Net 3.5). This is the preferred option because all code is running with the versions of dependencies they were compiled with.

2. Add a binding redirect. This will suppress the warning. However, your .Net 2.0 projects will (at runtime) be bound to the .Net 3.5 versions of dependent assemblies such as System.Windows.Forms. You can quickly add a binding redirect by double-clicking on error in Visual Studio.

3. Use CopyLocal=true. I'm not sure if this will suppress the warning. It will, like option 2 above, mean that all projects will use the .Net 3.5 version of System.Windows.Forms.

Here are a couple of ways to identify the offending reference(s):

• You can use a utility such as the one found at https://gist.github.com/1553265
• Another simple method is to set Build output verbosity (Tools, Options, Projects and Solutions, Build and Run, MSBuild project build output verbosity, Detailed) and after building, search the output window for the warning, and look at the text just above it. (Hat tip to pauloya who suggested this in the comments on this answer).

Basically this happens when the assemblies you're referencing have "Copy Local" set to "True", meaning that a copy of the DLL is placed in the bin folder along with your exe.

Since Visual Studio will copy all of the dependencies of a referenced assembly as well, it's possible to end up with two different builds of the same assembly being referred to. This is more likely to happen if your projects are in separate solutions, and can therefore be compiled separately.

The way I've gotten around it is to set Copy Local to False for references in assembly projects. Only do it for executables/web applications where you need the assembly for the finished product to run.

Hope that makes sense!

On Visual Studio if you right click on the solution and Manage nuget packages theres a "Consolidate" tab which sets all the packages to the same version.

This actually depends on your external component. When you reference an external component in a .NET application it generates a GUID to identify that component. This error occurs when the external component referenced by one of your projects has the same name and but different version as another such component in another assembly.

This sometimes happens when you use "Browse" to find references and add the wrong version of the assembly, or you have a different version of the component in your code repository as the one you installed in the local machine.

Do try to find which projects have these conflicts, remove the components from the reference list, then add them again making sure that you're pointing to the same file.

I just spent sometime debugging the same issue. Note, that issue might not be between different projects, but actually between several references in one project that depend on different versions of the same dll/assembly. In my case, issue was reference FastMember.dll versions mismatch that comes from two different NuGet packages in a single project. When I was given a project, it would not compile because NuGet packages were missing and VS refused to restore missing packages. Through the NuGet menu, I manually update all the NuGets to the latest version, that is when the warning appeared.

In Visual Studio Tools > Options > Build and Run > MSBuld Project build output verbosity: (set to) Diagnostics. Look for the line(s) There was a conflict between in the Output window. Below is the part of output that I got:

1>  There was a conflict between "FastMember, Version=1.5.0.0, Culture=neutral, PublicKeyToken=null" and "FastMember, Version=1.3.0.0, Culture=neutral, PublicKeyToken=null". (TaskId:19)
1>      "FastMember, Version=1.5.0.0, Culture=neutral, PublicKeyToken=null" was chosen because it was primary and "FastMember, Version=1.3.0.0, Culture=neutral, PublicKeyToken=null" was not. (TaskId:19)
1>      References which depend on "FastMember, Version=1.5.0.0, Culture=neutral, PublicKeyToken=null" [C:\Users\ksd3jvp\Source\Temp\AITool\Misra\AMSAITool\packages\FastMember.1.5.0\lib\net461\FastMember.dll]. (TaskId:19)
1>          C:\Users\ksd3jvp\Source\Temp\AITool\Misra\AMSAITool\packages\FastMember.1.5.0\lib\net461\FastMember.dll (TaskId:19)
1>            Project file item includes which caused reference "C:\Users\ksd3jvp\Source\Temp\AITool\Misra\AMSAITool\packages\FastMember.1.5.0\lib\net461\FastMember.dll". (TaskId:19)
1>              FastMember, Version=1.5.0.0, Culture=neutral, processorArchitecture=MSIL (TaskId:19)
1>      References which depend on "FastMember, Version=1.3.0.0, Culture=neutral, PublicKeyToken=null" []. (TaskId:19)
1>          C:\Users\ksd3jvp\Source\Temp\AITool\Misra\AMSAITool\packages\ClosedXML.0.94.2\lib\net46\ClosedXML.dll (TaskId:19)
1>            Project file item includes which caused reference "C:\Users\ksd3jvp\Source\Temp\AITool\Misra\AMSAITool\packages\ClosedXML.0.94.2\lib\net46\ClosedXML.dll". (TaskId:19)
1>              ClosedXML, Version=0.94.2.0, Culture=neutral, processorArchitecture=MSIL (TaskId:19)

Notice, that Project file item includes which caused reference "C:\Users\ksd3jvp\Source\Temp\AITool\Misra\AMSAITool\packages\ClosedXML.0.94.2\lib\net46\ClosedXML.dll"

ClosedXML.dll comes from ClosedXML NuGet and it depends on FastMember.dll 1.3.0.0. On top of it, there is also FastMember Nuget in the project, and it has FastMember.dll 1.5.0.0. Mismatch !

I have uninstalled ClosedXML & FastMember NuGets, because I had binding redirect and installed just latest version of ClosedXML That fixed the issue !

If using NuGet all I had to do was:

1. right click project and click Manage NuGet Packages..

2. click the cog in top right

3. click General tab in NuGet Package Manager above Package Sources

4. check "Skip Applying binding redirects" in Binding Redirects

5. Clean and rebuild and the warning's gone

Easy peasy

Another thing to consider and check is, make sure you don't have any service running that's using that bin folder. if their is stop the service and rebuild solution

I had such issue when my project had reference to NETStandardLibrary and one of referenced assemblies was published for netcore. Just published it as netstandard and problem was gone

Here's the solution, .NET Core 3.0 style: https://github.com/HTD/ref-check

When you find what conflicts, maybe you would be able to resolve the conflicts. If the conflicting references are from other packages, you either out of luck, or you need to use sources instead.

In my case, the packages conflicting are often of my own, so I can fix dependency problems and republish them.

I had the same problem. In the project's 'obj' folder I renamed the folder 'Debug' to 'Debug_OLD' and rebuilt. A new 'Debug' folder was built automatically, and the problem went away.