file(s) that can not be scanned for reason given by avast, are just that. it does not mean they are infected
many programs protect there files with passwords, like security programs, adobe… and many other

if you attach a screenshot of scan result we may be able to tell you what they are

these files will be scanned by avast realtime shield when they are accessed by the program that use them

files that can not be scanned is the most frequently asked question in the forum… at least once a week i guess
so if you search the forum, there is a ton of info