Lukor - I just checked, and MAYBE it's already working. Hard to say 100%, but looks better.
A reboot with sfc /scanonce did NOT show the Error 5 error message in System, and my test task worked.
Also, in Task Scheduler, when I right-clicked on avast! Emergency Update.job and hit "Run", I saw Avastem.exe as a process in my task manager (for a second).
But I still ask for advice how to make sure my Task folder is back to good (special) condition.
What do you think?