Agreed - the img unlockers do fail on the largest file of the GB Discoverer Full file. You can get it to work (I did) by copying the locked img file directly to your SD card and by then adding an UNL file to the SD card too. You need the patched JM keygen as outlined in post 10 of the Garmin GB Discoverer 1:50K - Full Coverage (2.00) topic (sorry I don't have enough posts to post links..yet)