Why wont VirtualDubMod read my joined video clips??

Ive got several little 5 sec video clips that i joined together using mpgjoin. the joined version plays just fine on my media player, but when i open the same exact file in VirtualDubMod for editing it only sees/plays the very first video clip out of the several that are joined?? why would this happen?? i even tried running the joined version through TMPGnc and it also will only read or play the very first small clip and coverts my entire joined movie into one little small clip?? whats going on??