VS 2010错误生成单元测试

I have one .NET 4 DLL for which I'm having trouble generating unit tests. I'm using VS 2010 Standard. Every other project in the solution will generate unit test stubs for classes just fine. For the other assemblies, I can go into the existing code, right click the class name, and select "Create Unit Tests". I get the selection window that follows just fine.I have one .NET 4 DLL for which I'm having trou