Yep, Garmin is still living in the past when it comes to the newer devices. Older models would only recognize a map if it was named gmapsupp.img. They really need to update their software to be smarter. Every Garmin device has a file named GarminDevice.xml that describes its capabilities. This file includes info that says whether the unit will recognize multiple map files. Unfortunately, Basecamp doesn't look at this file. If it did, it could automatically assign unique filenames so that the user didn't have to do this manually. Maybe some day they'll address this.