For each game, there can exist many different versions of it. different dumps, from different versions of the game, and even with different files inside the zip. FBA is very picky about the roms, and will only execute the exact version it has been programmed for. If a single file is missing or has the wrong name, then FBA does not want to run.
Also, some games (such as Neo-Geo games) need BIOS files to work. If you don't have the exact version of the bios, then FBA will not run those games.
This particular version of FBA (0.2.97.29) uses the same roms as MAME 0.149. We can't give links to the roms or bios files, so you will have to search for them yourself in the internet.
A "romset" is a pack of roms.