: Arcade ROMsets are updated frequently. If you have an older ROMset (like an old MAME set) but a brand-new FBNeo core, the core may no longer recognize the older file structure.
If you're aiming to contribute this information to the FBNeo project: romset is unknown fbneo fixed
To avoid "Unknown" errors in the future, follow these standards used by the FBNeo team Use Non-Merged Sets: : Arcade ROMsets are updated frequently