GAC and M$ Visual Studio .NOT
A colleague of mine was having trouble adding references to C# projects, of DLL's that are in the GAC. Apparently, M$ nows about this issue: http://support.microsoft.com/default.aspx?scid=kb;en-us;306149 I really love the last part: It is highly recommended that you not install your assemblies to the GAC, unless you want to share your assemblies with other applications running on that system. Also, note that it is not possible to directly reference an assembly from the GAC in your project. If you want to use an assembly from the GAC, you should drop your assemblies to a local folder, and then add a reference to the assembly from this folder.