The 510 (and the 710) had everything on a SD card. I still think you will want to get a new 2 gb card. You could try one now, or wait until you get the new SD card with app and map from TomTom.
If the "dhn resets" do not help, you are definitely dealing with corrupted files in the map folder. If you can't get past them using the new 2 gb card, then wipe it and copy over everything from the new TT supplied card.
You should have a good clean install. Make a good backup of it as-is, and then do the incremental item backups with Home I suggested earlier. This will make it easy to handle any problems in the future.
If the "dhn resets" do not help, you are definitely dealing with corrupted files in the map folder. If you can't get past them using the new 2 gb card, then wipe it and copy over everything from the new TT supplied card.
You should have a good clean install. Make a good backup of it as-is, and then do the incremental item backups with Home I suggested earlier. This will make it easy to handle any problems in the future.