Ensure the file neogeo.zip (for Neo Geo) is present. In a non-merged set, it may be separate. Place it in the same folder. FBNeo will automatically pull BIOS from parent ROMs or the BIOS file.
While a full 4,000-ROM set is impressive, 75% of those games are obscure mahjong titles, early black-and-white games, or prototype dumps. For a home arcade cabinet, consider building a "curated complete set" : fbneo complete romset
Romset organization comes in three flavors: Ensure the file neogeo