Last Friday I had the most infuriating day attempting to track down a problem with our project's continuous build machine. It was one of those erratic, inconsistent errors that prove tricky to pin down and it was occuring during registration of a DLL. The weird thing was Reggie and Regsvr32 were both reporting successful registration but MSBuild was failing in TlbImp when attempting to create the CLR callable interop wrapper from the DLL saying the DLL wasn't registered.
Anyway, I finally tracked down the problem on Monday morning when other weird things started happening. It turns out the Windows 2000 Server had run out of allocated registry space. (see http://www.google.co.uk/search?hl=en&q=windows+2000+registry+size)