Can you please try to unpair the device from the account (delete it on the my.avast.com) and from the device itself (Settings>avast account>upair) and pair it again? Thanks.
I deleted my device from Avast's site, then deleted the connection to my account on the phone. When I tried to reconnect to my Avast account (wi-fi enabled on my phone), I got this message: Your Avast! Anti-Theft installation is too old. Please update Avast! Anti-Theft before registering the device to your account.
Here's is what I did to try to to resolve this:
1. Tried to update the software from my phone, but was told it was up to date
2. Uninstalled Anti-Theft hidden file and Avast! Antivirus
3. Reinstalled Avast! Mobile beta, then downloaded Anti-Theft to my phone and installed the Anti-theft Advanced installation and renamed the file
4. Set everything up again, as I did for the original installation. Checked for updates, was told that software was up to date
5. Tried linking to my Avast! account again from my phone, but got the same error message as above