Would you believe it. After all the emails to and from avast and this extensive thread, I have just had a pop up telling me that my licence expires in 9 days. And I thought that I had another 3 years or or so. Promises, promises.
If your Subscription section shows the correct expiry date ?
Then check the system date to ensure that is correct and adjust as required.
If the system date is correct then try an avast repair:
Vista, win7 or later - Control Panel, Programs & Features, uninstall a program, select 'avast! Anti-Virus,' click the Uninstall/Change and select Repair, click next and follow.
You may need to reboot after the repair.
This has in the past resolved this out of sync issue between reported and actual information.