The type [X] exists in both...

You cannot imagine how fraught this compilation error was! On average every second launch of my web application I got a compilation error in Visual Studio 2008 saying

Compiler Error Message: CS0433: The type [X] exists in both [Z] and [Y]

Here is the according screenshot showing the compilation error:

And the compilation error was true. When inspecting the mentioned DLL's with Lutz Roeder's .NET Reflector the type [X] was actually present in both. But why? I checked all my files whether there could be some naming conflict or similar...nothing. And the best of all: the error happened only on my PC and on one other team member, but not on all of the other team members although they were working on the same code (using TFS). Doing a clean of the solution and a full rebuild resolved sometimes the error, often I had also to delete the whole "Temporary ASP.net files" folder. It was frustrating because often I had to repeat the clean all & rebuild 3 to 4 times until I was finally able to launch the application. This consumed a lot of time and I was already under time pressure due to the strict project plan. I asked several people, wrote in web forums but it seems as if nobody had a useful solution beside the usual hint of doing the clean & rebuild.

Now, since 3 days the error disappeared! As I heard our system administrators have installed a couple of service packs and updates under which they've also installed one for Visual Studio 2008. I'm not sure which of the updates solved the problem, but probably the one for Visual Studio. So if you have a similar problem, give it a try, it may solve it and save you a lot of time.

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