I recommend manually updating (as said above), once that is complete, start Avast, open the chest, re-scan each file in turn, and when (if) it scans clean select "restore". A copy is retained in the chest; there is no indication restore is taking place, but it does. Check each original location to be sure before deleting it from the chest.
This won't work for everyone. Some people are unable to boot. I think the questions will roll in for a while, yet.