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!

I wanted to post pauloya's solution they provided in the comments above. I believe it is the best solution for finding the offending references.

The simplest way to find what are the "offending reference(s)" 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. See the text just above it.

For example, when you search the output panel for "conflict" you may find something like this:

3>  There was a conflict between "EntityFramework, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" and "EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089".
3>      "EntityFramework, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" was chosen because it was primary and "EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" was not.

As you can see, there is a conflict between EF versions 5 and 6.