Hello,
5 minutes ago I got the following message (see attachment) during a manually started full scan.
What does it mean to me?
No idea but something that may help others here is a rough translation from the German of the AVAST message at the bottom which apparently states that:-
“The scan could not be started . A file can not be created if it already exists.”
Shot in the dark.Check disk for errors and bad sectors.
You may get better help if you post in your native language.
Find your language here https://forum.avast.com/index.php?board=21.0
Oh, I’m sorry. :-[
“Check could not be started. A file could not be created, because it exists.” 
Perform a repair of avast and try again.
If that doesn’t solve it, perform a clean installation of avast and try again.