@andrewcoughlan Ok - I just tried the 4.2 basic image and it's worked fine. There's something I've done with my images that's throwing it out but I'm just going to rebuild my image and test along the way. Thanks DankCushions for your help!
BTW.....can I set this for the MAME (Mame4all) emulator...? I didn't see it listed in the RetroPie Setup options.