When adding a service reference in Visual Studio 2008, I came across a weird error. The reference was created successfully, but when I tried to build the project (a c# class library project), I always get a custom tool error ("the global element ... was defined in both ... and ..."). Thus I could not compile. Everything I tried didn't work. After reloading Visual Studio I got another error (Class ... is already defined in another namespace).
I finally solved this problem by deleting the Visual Studio project, creating a new project and adding the same service reference a second time.
I don't really know, what caused this error, but maybe it has something to do with changing the namespace or the service reference name after the first creation.