It doesn’t matter whether another Anti Virus/Security program is activated or not, there will be potential for conflict.
I recommend you use the Norton Removal Tool and follow all directions.
https://support.norton.com/sp/en/us/home/current/solutions/kb20080710133834EN_EndUserProfile_en_us
Then see if a Repair will complete.

If not you will then require a ‘Clean Install’ of your Avast product:

Down load ‘and save to your desktop’ the Avast Uninstall Utility here: https://www.avast.com/en-gb/uninstall-utility

Download to your Desktop your correct Avast version from here: https://forum.avast.com/index.php?topic=178580.0

Now disconnect from the Internet
Uninstall Avast via the Control Panel

1.Run the uninstall tool and accept the reboot to safe mode
2.Once complete reboot your system
3.Reinstall Avast