: Your ROM set may be obsolete or meant for a different emulator (like an older MAME version). FBNeo is frequently updated, and some games change their internal file requirements over time.

For systems like Neo Geo , you must have the neogeo.zip BIOS file in the same folder as your games. 4. Perform a Manual Scan (RetroArch)

Arcade emulation is different from console emulation (like NES or SNES). Arcade hardware was constantly changing, and as developers learn more about the original chips, they update the emulator to be more accurate.

Here is the definitive guide on why this happens and how to fix it for good. Why FBNeo Says Your Romset is "Unknown"