Mame roms are a lot to take in. Some roms need a 'parent' rom in order to work. These games are usually revisions of other older games. I don't know which rom you have for Mortal Kombat but it could require the parent rom to work. In the link I posted, if you look at the compatibility list for each ...

From time to time, individual roms are updated to reflect changes in the way they were dumped or a change in the understanding of the original hardware they ran on. Because of this, each version of Mame that comes out may have a slightly different rom its looking for. Therefore you have to match the...