The same thing was happening to me yesterday. My profile file must of got corrupted. I transferred my profile file from a 2 week old backup to my Curve and that seems to have fixed the problem. The backup profile file from last week would allow me to do one backup then I would get the error message on a second backup. When I used the 2 week old file everything seems to be fine.
You will find the thread I created here Backup errors out