OK, the last image says it all
In the Area selection dialog, you've checked the "Logitech QuickCam" item (which is probably some kind of a virtual folder for the operating system). For some reason (unknown to me right now), it produces this strange path... which avast! is unable to scan later, when you start the scan - because this path is completely wrong.
So, the "fix" is very simple - don't check the QuickCam "folder", it doesn't have much sense.