Just to add to this, if your getting the "13b bad" with xmen 4 player on retropie on raspberry pi3, I needed to delete the xmen.nv file from roms/arcade/fbneo - I had been using FBA but updated to FBneo the romset I had didnt work but this thread got me looking for spurious files and led me to this, as soon as I deleted that file it worked perfectly, so thanks OP!