Two items come to mind.
is this a BulletM2HP or an earlier model? The prior models do not have enough memory to load BBHN and are not supported.
Are you using the bullet "factory" .bin file or the "sysupgrade" .bin file? For a new Bullet with AirOS on it you need the "factory" .bin file. The "sysupgrade" is for devices that have been previously flashed.