I assume this is a COM dll, otherwise you could just put the dlls in the directories with the apps and it would be fine. You've done the wrong thing, and there's no easy way around it. If you're going to change a COM dll, you need to generate a new GUID so you have a new version. Either way, you should never break existing functionality, only add new functionality. In .NET, dlls are not registered, and are just loaded from the local directory. This change was made because the recommended way to use COM would work fine, but too many people just didn't bother to do it properly/thoughtfully.
Christian Graus - Microsoft MVP - C++ Metal Musings - Rex and my new metal blog