If you are using Windows 7 backup and experiencing difficulties please see the KB articles all of which have hotifxes:

Backups fail and Event ID 12293 is logged on a computer that is running Windows Vista or Windows Server 2008

You cannot back up a file in Windows Server 2008 R2 or in Windows 7 if the path length is longer than 260 characters

The backup process requires significantly more time when you use the Windows Backup utility in Windows 7 if the size of the backup files increases