Access 2003 upgraded to 2007 now get error ''Class not registered''.

Access 2003 upgraded to 2007 now get error "Class not registered". Probably a Reference not loading? All updates done. Still using mdb file structure. Compiles OK. ## Deliverables The problem is probably my PC and not the file since it worked for years under 2003. The goal is to have it working without this error on my PC. I'm using vista and have done all updates .