Are you using the trial version for 2 months? It'll expire the trial period.
Register for free and add the license key into avast.
David has already paid for the Pro license, see below.
I recived a licence number when i paid for the 1 yr subscription in feb - and used the link to download
So I suspect that he may not have entered the license key into the about avast, License Key area, as Igor is I believe surmising.
@ David
Have you received your email with your License key ?
If so have you entered the key into your copy of avast ?