I recently had a C++/CLI project start throwing 351 instances of the C4945 warning on me. The project references 3 C# assemblies, "A", "B", and "C". I suspect the problem comes in because both assembly "C" and the main app reference assembly "A". So when symbols from assembly "A" are imported into the main project at compile time, those warning get thrown because those symbols already exist via assembly "C"'s reference to assembly "A". Hence the message text: "Cannot import symbol ... from assembly ... because the symbol was already defined in assembly ..."
Microsoft's KB922271 article suggests setting "Copy Local" and "Copy Local Dependencies" to false, which accomplishes nothing in this case -- nor does installing the related hotfix.
What I stumbled upon was that setting the "Copy Local..." options back to "true" and setting the "Use Dependencies in Build" and "Use In Build" options to "false" solves the problem. From there, I would guess that taking the reference to assembly "A" out of the main project would also solve the problem, though I haven't tried it yet.
The weird thing is that I have two machines on which I develop this project. Only one of them ever generated this warning message. So I'm not sure what the internals are that cause this message to/not to show up.
But the bottom line is that I would check your references, and see if you have two projects in your solution both referencing a third assembly. That seems to be the root cause.
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