I got my refurbished Montana 600 unit today. I liked it a lot, good value for money. After play around with it for a while, I started pasting unlocked maps I downloaded from various places on the internet. As usual, I paste .img files to SD\Map folder. I thought those maps would work. However, to my astonishment, none of those unlocked maps ( City Navigator, Blue Charts g2, Topo, etc ) would work. The screen prompt is : Can't Lock Maps! I then tried to copy those maps to internal memory of the device, under Garmin directory, still no luck. Can someone help me with this situation?

Possible causes:
1. The original firmware was 3.80 and I updated it immediately to 4.60 when I got the device.
2. The unit is bought in US, but I am in Asia. So I can't even register the unit in MyGarmin dashboard.