1st time quick scan came back saying Some files could not be scanned. The scan last week was fine. I updated security passwords on many accounts during this week, could this have caused the warning? What action is necessary ?
Have you changed the default settings in the Quick scan ?
The reason I ask is because archives aren't scanned by default as they are inert and don't present an immediate risk.
If you haven't changed the default settings then we need more information on the file name and location.
Files that can't be scanned are just that, not an indication they are infected or suspect in some way, they just can't be scanned. If the program that assigned the password were to unpack the archive, they are no longer protected and avast can scan the extracted files.