I used Mapupdater v3.2.2. It re-downloaded all the map content (it uses a different download directory than Garmin Express), but refused to install to the device, giving me the same error message as Express.

Kunix has graciously helped me restore my model # to 2460, and I was able to install the complete map set via Express.

The levels of helpfulness & expertise on this forum are truly astounding. I have learned a great deal about Garmin GPSs over the last 2 days.

I do have 2 questions, answers to which I think would be extremely helpful to people encountering similar issues:
Is it possible to clear NV memory in a non-bootable device without erasing the entire rgn41?
My current GarminDevice.xml (and hence, I'm assuming, rgn41) is missing the RegistrationCode and the Unlock Codes present in my original one. I seem to be able to install maps my device is subscribed to without an issue. Are there any ramifications to the missing information, and is there a way to re-populate the NV with it?