May not work at all
Windows 7 Backup appears to have been spawned from the fertile mind of some engineer inside Microsoft who had never encountered a real backup program and had no idea what a real backup program was supposed to do or how it was supposed to work. (Flame off -- sorry, but I have designed a backup program before that is still being sold, so yes this is my opinion, but it's an opinion based on been there, done that, if anybody on my team had come up with a design as lame as Microsoft's built-in Windows Backup I would have fired them on the spot).
So anyhow, I was getting the exact same error from Windows Backup. I did the recommended chkdsk /r on the external USB3 hard drive, no problems. I also checked the Windows logs, no problems reported there either. So I attached the drive to my Linux server and exported it to my Windows system via iSCSI (one thing Microsoft *did* do very well was their iSCSI initiator, which is the best on any OS anywhere). That way I could check the Linux logs to see whether it was encountering any actual I/O errors on the USB drive. And don't you know it, about 18% of the way through, Windows 7 Backup gives me this error *again* -- and there's no errors at all reported on the Linux side, which happily tells me that the drive is fully operational and all hunky!
Checking the Microsoft tech support forums, it appears that this issue has been reported repeatedly to Microsoft multiple times since 2008, with various ineffectual handwaving on the part of Microsoft as to why it happens but no solutions. My only solution was to roll my eyes, do a network backup to a network share, and start investigating a real backup program... which is a topic for another post.
So a) run a chkdsk /r on the drive (or the GUI equivalent, right-click on the drive in explorer, go to Tools, and tell it to check all blocks), but b) know that it may never work and Microsoft has no solution if it doesn't, they will just handwave that it must be someone else's fault. Which means c) the solution is likely another backup program. So it goes.