Hi all,
I had the same issue. I tried everything that I had read on forum threads but nothing worked. I eventually contacted HTC and this is what they said...
under settings > power, you have to disable the fast boot option. Then, turn off the phone and restart it after 5 seconds.Try backing up after the phone after it has rebooted. Most likely, it won't work but give it a go.
If the above doesn't work, restart your phone in safe mode. You can do this by turning off your phone and while booting, keep the 'volume down' button pressed. This will launch your phone in safe mode (you will notice the safe mode box on bottom left side of the screen). Safe mode disables all 3rd party apps and shows only HTC content. Try running the backup now and it should work!
The down side is that now, you will need to isolate the 3rd party app which might be causing an issue for failed backups.
Let me know how you guys go.
Thanks!