I made my regular update, from iOS 6.0 to iOS 6.1. When I try to restore my previous back-up, this error appeared, 'iTunes could not restore the iPhone because the backup could not be saved on the computer'. It came right after Low-Disk notifications from Windows. I cleared up some 4gb of space from hard disk to make it available for 20gb space but the same error occured when i try to restore again. I'm using Windows XP and iTunes 18.104.22.168. Thanks for your concern, please help me on this issue.