Cause:
This error is most often the result of an unstable USB connection, which causes the data transfer between phone and PC to fail at random points during the update process.
What to do:
Switching to a different USB cable often helps, as does trying a different USB port on the PC, or a different PC altogether.
For backup failures specifically, you can also try reducing the amount of content on your phone temporarily. For example, delete any synced media from your phone (leaving it on the PC),
perform the update, and then re-sync the media content back to the phone.
