When I run Windows Backup to an external hard drive with administrator account on my Surface Pro, I get error code 0x8078012D and the complete backup fails due to i/o after approx 80%. Try chkdsk command, disable antivirus and different HDD still can’t get it working.
How to fix Windows 8 Backup Error code: 0x8078012D issues on Surface Pro
* Press Win + X keys together and select “Computer Management” option. You can also open My Computer and click on “Manage” button in the ribbon.
* In Computer Management window, click Services and Applications > Services
* Search for “Volume Shadow Copy” in the right list. Right click on it > select Properties > change the Startup Type to Manual, and OK button. Repeat the same for Windows Backup service.