Originally Posted by
L Beezy You may have to delete the previous backup in order to backup your phone. You can do it in apps+settings. go to Manage Backups and delete that backup. Once it deletes, then hit "back up now." Your phone should now be able to back up correctly.
I had this issue prior to doing to the Denim update. Could not figure out the backup wouldn't work. Searched for awhile, and found a response like this somewhere here, which fixed it for me, allowed me to do the backup, then the update.
These are the types of answers that can make your day.