If you have uploaded your mame4all roms but none of them will play, you need to follow these steps:

1) remove the default mame4all roms directory

rm -r ~/pimame/emulators/mame4all-pi/roms

2) create a symbolic link that points to your real mame4all roms directory

ln -s ~/pimame/roms/mame4all ~/pimame/emulators/mame4all-pi/roms