As well as other *.gcd files, do a search for any *.zip files and delete them all. If that doesn't work then cut to the chase and just reformat it with RMPrepUSB, you'll be able to replace most required files/maps with GE and anything it doesn't give you like the basemap (gmapbmap.img) can be taken from your backup. If you do have to format and it doesn't boot, create a folder named Garmin in the root and try again. Some devices won't boot empty.