My laptop has been backing up once a week fine (except for an error about a missing file that is on the target drive, not the backup drive) for months. In the past few days, it has suddenly failed with repeated attempts to backup, it always stalls at 57% while creating a system image. I've tried a clean boot, same results. I'm backing up to a network drive (USB hard drive attached to the router), 274GB free of 458 total, and the total backup size has been pretty small as no heavy data is kept on the computer.
Windows 7 Professional
Any thoughts on why the sudden failure?