Hi,
Please refer to the following article first.
You may receive error messages when you try to perform a backup operation on a Windows Vista-based computer
http://support.microsoft.com/default.aspx/kb/950167/en-us
If the issue persists, I suggest further discussing this issue in the following forum:
Backup – Windows and Windows Server
http://social.technet.microsoft.com/Forums/en-US/windowsbackup/threads/
I hope your issue can be resolved soon.
Tim Quan - MSFT