The problem is new nuvi models have a protected firmware that looks for a digital signature in Garmin maps, if you unlock a map with new gimgunlock+mapsigpatch or other available unlockers this signature is removed and you'll get a message the map is corrupt.
Old unlockers wont work either.
Nothing to do actually, you must use free maps or buy Garmin maps for nuvi 2597.
Formatting it is useless in this case.