I suggest you add ashWebSv.exe to the exceptions.

What browser are you using ?

Do you have JavaScript enabled ?
It is required the link works for me, it pops-up a window and then I get a download notification, see image.

I’m not sure if a clean reinstall would resolve this ‘if’ it is related to a NAV remnants issue, but it won’t hurt to try.

Download the latest version of avast http://www.avast.com/eng/programs.html and save it to your HDD, somewhere you can find it again. Use that when you reinstall.

Download the avast! Uninstall Utility, find it here and save it to your HDD.

Uninstall avast, reboot, run the Uninstall Utility, reboot, install latest version, reboot.

You shouldn’t need to re-register if you still have the email you were sent with the registration key.