That error means that there is something wrong with your windows installation.
Microsoft's support site has many posts about this kind of problem, where the solution varies according to how the user got there. Try googling for
0x80070002 windows 7 backup site:microsoft.com
Almost all of the replies I looked at started with a suggestion that you run file system check. That is a good thing to do regardless, so you might want to start there. To do a check, right-click on the drive (probably C
, select properties, then tools, then "Check now". It will probably complain about not being able to do the check at the moment, asking of you want it done at the next reboot. Say yes.