I know where is the problem, its come from the Multi-language download file.
I got the same problem with register online to get license.
To fix the problem, i uninstall avast, redownload french version only and the problem gone…
Try to download the English version only not the multi-language one.
I test it on 3 computers and they fix all of them.
I hope that will help you guys.
JS
IT Technicien