Go to "my computer" and into the device "Garmin" folder, delete the file "gupdate.gcd".
Edit your device.xlm in this line:
00</PartNumber><SoftwareVersion>XXX</SoftwareVersion><Description>nüvi
Put in it a previous version than the one you want to flash it to-
Add your desired version gupdate.gcd in nuvi ,disconnect nuvi from pc and restart it.
To check file HWID use
[Only registered and activated users can see links. ]
drag&drop the gupdate.gcd in it and it will display infos