Pondus
2
Files that can not be scanned does not mean they are infected, it is just a scan error message and avast tell you why
There can be many reasons why they cant be scanned, it is normal and happen to all security programs, but all programs does not show it in the log
avast realtime protection will check those files when whatever use those files unpack/access/read/save/use them … avast realtime constant monitor evrything in your computer when on
This is the most frequently asked question in the forum so lots of info if you search
How do I handle files that avast! can’t scan? https://blog.avast.com/2014/02/28/how-do-i-handle-files-that-avast-cant-scan/
they seem to be windows update files 
How to Reduce the Size of Your WinSXS Folder on Windows 7 or 8 http://www.howtogeek.com/174705/how-to-reduce-the-size-of-your-winsxs-folder-on-windows-7-or-8/