Unable to Complete Backup - Error 0x80070002

I had the same problem for weeks. No solution described on the net helped me. Neither registry changing, nor Windows-Patch from Microsoft -sites, nothing. My really solution was activating the Windows partition (by me this is the drive C:) via partition manager (Start menu -> search "Create format and hard disk partitions" -> ENTER -> Disk Manager comes up -> right click on the partition which has booting Windows system -> "Mark partition as Active" -> restart the system -> backup worked successfull again). Yes, the strange thing was here, that the system partition was not active ! Only this change helped me. Try out! It should help you!

Hello, I've been having the same problem for months. Initially I though it might be associated with my external hdd but it is not. It is a huge inconvenience. It happens both on my laptop AND on my desktop (same OS).
All Backup attempts fail after they have (successfully?) completed the 99% of the process and I get the message that "Backup completed but some files were skipped". BUT in fact nothing is backed up! (The latest backup still dates 5 months ago despite attempting to do Windows backup numerous times since then. The skipped files were 2, related to my email account I have setup on Outlook. (Of course I have tried with Outlook shut down). Help? Thanks!

@endree suggestion is scarcely credible (not endree but Microsoft). Why should an update to the Master Boot Record (MBR) have any bearing on a backup that doesn't even include a Windows image !? BUT IT DOES and the suggestion worked for me too. After updating the Active Partition as suggested, I couldn't boot from HD and had to effect a Windows repair from the Windows 7 installation disk. This found a problem with the MBR and re-wrote the record. Backups are GO!

@TSeeker - nice diagnosis and approach to the problem - very professional. It looks like your complete re-installation of Windows did the trick because the MBR would have been re-written during the whole tortuous process. Sorry to hear that you had to go through so much grief.

I just wanted to chime in here and confirm what papertape is saying. I had the same issue, activated my C drive and had to repair the MBR with a repair disk so FYI, be sure you have a repair disk before proceding