I cant get the roms working on my mame4driod emulator?

Im trying to get games on the Mame4droid working, they appear in the games list but every time I try and run the game but it says the game is missing roms or CHD images. The files were added zipped so not sure how they could be missing any files?? Any idea if there is an easy fix or is it just luck with the files? Please help.