now in this i got experience, what you have to do first is to find a place where you can find the mame rollback roms, cant tell you where to get them but you can search for a torrent (if you know what that is) because its a big download , 5gb , once you find that and downlad the whole thing, then you can use clrmamepro to rebuild your romset back to mame98, after that , you will have to rebuild your gamelist if you are using a front end, remeber its [romsite name hint redacted]