While we are not exactly talking the same type of DLL (or COM) your answers helped me after three days of searching! I had an app that needed to be invoked from Excel 2000 VBA code. My problem was: I could invoke NET Framework 1.1 DLLs but not the NET Framework 2.0 DLLs. As you stated, something went wrong when they created Framework 2. I could not even do this using Excel 2003. Since we upgraded to Visual Studio 2005, I had to get this call from Excel working or it was back to redesigning a major part of our application. It also deals with customer credit card numbers, therefore I could not have cut the usual corners I wanted to.
Thank you for posting the question as well as the reply. I hope you see this, since you posted it last year Dec.