Once you've downloaded a North American .GMAP folder using GarminExpress linked to a device (say your nuvi 55LM) there are codes also downloaded and installed limiting the use of that map data to compiling IMG files for only the device/s authorized under those codes. So if you then hook up your nuvi 205 for example which has no map update entitlement you're not going to get a usable map unlocked for the device. Even if the GMAP folder has been unlocked for use by MapInstall the resultant IMG will still be locked so you then need a modern IMG unlocker. Search for "gimgunlock V0.04", you won't find it on this forum. Quite frankly the simplest way is to send what you need to an SD card where it will be loaded as gmapsupp.img in a Garmin folder, remove any .GMA files also loaded and then run gimunlock on the IMG and it'll be usable in any device without modern protected firmware.