Oh, then do this: Get a 16GB or 32GB FAT32 card, make sure it's clean. Create a folder Garmin on it then copy and paste your GarminDevice.xml from the unit into it. Ensure GE is not running in the background [minimised to the system tray] if it is exit it completely. Plug the card in a reader into the PC [you can also use a usb flash drive], start GE and it should detect the card as the nuvi and complete the update. Delete the .xml from from the card if using the same card. You can leave some files such as JCV and ASR on the card but move them into it's Garmin folder, or use another smaller card if necessary. If you have any *.srd files in the card's ASR folder they must be moved to the unit's .System/ASR folder though, leave only asr/srx files in Garmin/ASR on the card. Move everything else including the map's associated files like .gma to the unit and other files/folders as appropriate. Make sure you observe correct placement, reflect the order in the card on the unit and you won't go wrong. You can move any gupdate.gcd off the unit to a backup location on your PC too for a bit more space.

That way by using the asr/srx and jcv file on the card there should be enough space on the unit for the map. Some other minor files normally in .System will also work in the card's Garmin folder but not Voice, Vehicles etc so have them on the unit. If worst comes to worst you may have to leave the detail map and its associated files on the card in a Map folder. Even the basemap should work in the card's Map folder and the 3D building image certainly will. Experiment a little with placement and it'll all work eventually.