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I don’t know if you have some malware, but I would first do the simple thing suggested there: run the complete setup.exe.
So, please download the latest STABLE version of Avast (the same edition you have, AIS).
Just in case, make a backup of your license file of Avast. Then close any other program, and run the new downloaded setup.exe of AIS. Once the installation finishes, please reboot immediately.
Once rebooted, go to Avast main GUI → maintenance → registration, and review the info there so to be sure your original valid registration is still recognized.
Please, don’t skip any of the reboots I just suggested.
Then use your system as normal. If you find out that future updates are having problems, report back.
After a couple of reboots and normal use, you might want to run a new scan, just to be sure.