MAME problems

I just downloaded the MAME4all emulator, installed it in the psp and it came out fine. I got a hold of some roms for it (mainley Marvel vs capcom, oh yeah thanx for the link 4 the capcom emu but it didn't work) went to put the roms in the specified folders (game 150 folder, MAME4allpsp folder w/o the percent ) but the screens comes up black says error no available games found please help, what I'm I doing wrong