I successfully recovered it from 5.7 back to 5.4 after delete the GCD file in system folder in the device. But it still can't recognize the map. Now, the device looks well for everyting except the maps issue. I tried to creat a unl file containing code generated by Garmin Unlock Generator 1.5 or unlock the img directly with GarminUnlockerAlternativev6.02 but failed. Before that, both methods worked well. Does anyone have any ideas for it?