I just unlocked Benelux_Cyclemap.img with Fast Image Unlocker as written in post #1, no problem. But I use TotalCommander and cmd (still like dos-commands), no problems with hidden extensions.
In the *.img file are 4 unlockcodes written !. I just removed them with Gmaptool. Also split this file for use in Mapsource: No search for places, but good for making routes and tracks.
Put the img on usb stick or gps, connected to PC and you can use the map in Basecamp (still learning Basecamp, I prefer Mapsource).