iTunes cannot backup iPhone because an error has occurred
The title is the error message I receive when syncing/backing up my iPhone. I love the error message its so specific as to what the problem could be.....
Itunes>Preferences(under the edit menu)>Devices>iphone backups...delete any and all backups listed. Connect your phone, itunes running, right click the phone in the device pane & select "backup".
If this has happened again, I'd suspect corrupt data on your phone, that of course gets transferred to your backup when such is created, thus preventing you from updating that backup. Your only choice to get out of this cycle would be to again delete all existing backups, then restore your phone as a new device in itunes, followed by syncing your itunes content back to your phone. When prompted to create a backup before restoring as new, decline. This will erase all data on your phone.