Nuvi 2360 have GMA protection, you have to unlock the map with one of the unlocker tools, this protection is not present in MobileXT thats why you can use the UNL file to unlock in XT but not in Nuvi.
try to unlock the gmapsupp.img with Fast Image Unlocker and put the file in Garmin folder in SD.
If you use the map like gmapsupp.img the map can only be copied in SD:\Garmin folder. Only one gmapsupp.img can be in this folder.
If you use the map with personal name for exp europa.img and copy it in SD:\Map folder you can use more maps in SD