Your ROM is outdated, mismatched, or renamed compared to what this specific FBNeo build expects.
: Systems like NeoGeo or NeoGeo CD require specific BIOS files (e.g., neogeo.zip ) to be present in the same folder as the ROM or within the system/fbneo directory. Troubleshooting Summary File unzipped Re-zip the files or disable "Extract ROM" in your frontend. Old ROM version Acquire a matching FBNeo romset instead of a MAME set. Frontend conflict romset is unknown fbneo fixed