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One of my solutions is making the Roslyn bits throw fits in VS2013. I've attached the solution code, hopefully this can be reproduced. Seems like it may be related to just viewing some files, but building the solution always reproduces the crash.
This is all I get from VS for information:
System.ArgumentException was unhandled
Message: An unhandled exception of type 'System.ArgumentException' occurred in Microsoft.CodeAnalysis.Workspaces.dll
Additional information: An item with the same key has already been added.