Avast needs to warn users about this problem!
I spent almost two full days trying to fix System Restore failures on Win8.1 64-bit that were apparently caused by Avast, though Microsoft diagnosed the problem as, "This is due to the system boot files are missing or corrupted." (
http://tinyurl.com/qf4nlnm). I eventually reinstalled Win8, restored a System Image backup, and when I found that System Restore still didn't work I completely removed Avast and finally System Restore worked again.
This was so time-consuming because:
- Early in the process I googled "system restore 0x80070005 site:avast.com" but didn't come across this post or anything definitive
- MS said boot files were the problem
- Attempting System Restore in safe mode also failed, and I expected Avast to be disabled in safe mode
- Disabling Active Protection shields appears to disable avast, but apparently doesn't
KevTech's suggestion to use System Image Backup makes sense, but it's not at all obvious, buried as a small icon in the lower left corner of the "File History" Control Panel item. The "Enable Avast self-defense module" check box isn't at all obvious either under Troubleshooting.