Eeek, don't go copying those dlls around....
Plug-ins get registered in the registry. Then the typical apps read the list out of the Windows registry. When a new plug-in gets installed, they should appear in the list.
Did you by any chance just copy the DLLs off of another system and expect them to work by putting them somewhere?
I suppose it's possible some plug-ins might not install themselves properly... also that the check-the-registry process might not be perfect...
I know that someone had posted a way to make sure something appears in Cakewalk's list. Perhaps the same steps apply here except for the names of any Cakewalk-specific registry keys, if any...