Can someone here explain this to me
Every file being detected here is part of Avast. Do I need to delete these files or not?
Well to start with there are NO DETECTIONS here, but files that can’t be scanned and the reason the files can’t be found.
These all look like the avast housekeeping removing the old definitions sub-folder (from yesterdays defs) and its contents.
You can’t delete them as they aren’t there and the Apply button is greyed out. But the bigger reason is why would you want to delete a file that can’t be scanned. That isn’t an indication that they are infected or suspect.
Oh. Just asking for confirmation! My question is that why would Avast detect these files that can’t be scanned, can’t be found, and just like you said I can’t delete them as they aren’t there. Avast! should make an improvement in their scanning mechanism 
As I have said these aren’t detections, but simply a report of what files can’t be scanned and why.
How can it possibly scan something which is no longer there ?
There is nothing wrong here or that needs improvement as you can’t scan what has been removed between the scan starting and it getting to that location.
My question is that why would Avast detect these files that can't be scannedas David say, scan errors are not detections..... and i guess the reason for this is that there is a reference to those files somwhere, but when avast scan engine gets there....nada files not found error is usually gone if you reboot and scan again ;)
Avast! should make an improvement in their scanning mechanismyou mean it should be able to scan files that are not there ..... hmmmm....avast may need som help from Harry Potter with that ;D
LOL Harry Potter yeah i second to that that includes Hermonie and Ron :). I guess I have to just except that guess no need to do any scanning improvements and things like that