Welcome to Justanswer.com, my nameis Dustin and I will do my best to assist you.
The only way to undo this error. Is to leave the gps on and let it run out of power. Once it runs out of power, we then will need to reconnect the gps and then delete the gcd.update file, that way it can reinstall the map successfully!
I realize as part of this process we wont be able to continue for another 4-8 hours until the device completely drains power. So when that happens youre welcome to get back to me, as we dont want to try the update again until we have removed the faulted file.
Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.