If using the FBNeo core, check the "Information" section to see which ROM set version it expects. 2. Use a ROM Manager
FBNeo expects sets by default (depending on compile flags). fbneo romset unknown
FBNeo supports consoles (Mega Drive, NES, ColecoVision). Ensure your console ROMs aren't zipped if the emulator expects a specific extension like .md or .nes , though for arcade games, If using the FBNeo core, check the "Information"
, ensure your core and your ROMs are from the same "release" cycle. If you updated your RetroArch cores recently, your year-old ROM set might suddenly show up as "Unknown" or fail to load. Do you have a specific game If using the FBNeo core