Since several days during compilation i had the error: Cannot register assembly "Foo.dll". Exception has been thrown by the target of an invocation. In the output-window with diagnostic compile information the following statement was listed: Foo -> Foo.dll C:\WINDOWS\Microsoft.NET\Fr... error MSB3217: Cannot register assembly "Foo.dll". Exception has been thrown by the target of an invocation. Done building project "Foo.csproj" -- FAILED. Manually ......