I have brand new computer, with Win10. Everything worked fine in my old XP, but “scheduling” of Scans has not worked in my new computer. I used to do scans at 10:10 each Tuesday and Friday. None has been done in one month. I made a phone call, and the support person did not understand what I said, but said that Avast was improperly installed, without telling me why.
Is anyone understanding or having the same issue? Also Win10 insists that I have older versions of Mozilla Firefox and Thunderbird.
Well the first thing that comes to mind is whether or not the “brand new computer” came with an Anti Virus program PRE-INSTALLED and whether it was removed by venders Unistall Utility BEFORE installing Avast? ???
Excellent question, because I, just found out that McAfee was still on the computer, though disabled.
But, why is Avast working in every other way.
I will remove McAfee, and seee if it makes any difference, and, then, report.
And run McAfee removal tool
How to uninstall or re-install supported McAfee products using the Consumer Products Removal tool https://service.mcafee.com/FAQDocument.aspx?id=TS101331
I had LiveSafe. Uninstall completed, removing everything, including Registry Keys.
Scheduled scan did not start. So, I created another one. Will see if it works.
Nothing happens. I tried to change times, twice, and the Scan does not start.
I may want to uninstall, and then reinstall, but why should it make a difference?
May bre it is a Registry foul up, as I see it for iTunes.
Maybe you should have followed the instructions Pundus posted. 
If it is not enough to uninstall McAfee, and remove any traces of it, I might as well give up on Avast. I don’t have a clue on which password I had to McAfee. I can’t believe this. But, I will try something.
The problem isn’t Avast. The problem is properly removing your prior AV before you install a new one.
I did not reply before, because I got Avast to start a a Scan, as scheduled, twice, this month. I schedule scan twice each week.
So, it is not Avast! I decided to give up on it. It is lot easier to give up!