I have tried requesting an offline key by email. But it shows the key “is not a valid licence key” message after I insert it.
So how does one register free version 9.0.2021
Not work
http://i.imgur.com/6OEga8C.jpg
Mirror Image link
https://imageshack.com/i/nmzx6lyj
Right click on the little avast icon in the system tray, then click on registration information. You should be able to register the free version without any problems.
computer not connect internet 
pc/2
what AV did you use before installing avast?
did you uninstall it before installing avast?
General: Uninstalling a third-party antivirus software http://www.avast.com/en-eu/faq.php?article=AVKB11#artTitle
How to register avast! Free Antivirus 2014 ? http://www.avast.com/en-eu/faq.php?article=AVKB9#articleContent
@Nick2…You can’t connect to the internet?
I try it does not work. You try it or have Administrator rights.
Before you answer the question suggests, test and see.
You need version 9.0.2018.
http://www.oldapps.com/avast_antivirus.php?old_avast=14679
Then insert the key from the email. Then install 9.0.2021
I didn’t have to have a license key to register the free version.