I get the same error including a popup my database would be outdated and i may want to update them.
I am happy to know it isn't a personal thing against my PC. My guess is that some group of various 'anonymity' is DDoS'ing the servers, or another illicit overflow variant so they can push their own 'modified' update out to Avast clients; most likely the business ends but with how much of our lives our connected to us electronically, it could be aimed at home users too... and yes, that is just an opinion since I don't have access to the Avast server logs.
I did just recently post some exploits (the type and methodology behind them that is) happening on XBL and FB and Netflix (its a combined, multi-site technique similar to how MyCandianPharmacy used to make their web sites from multiple servers in Op:Ghost Click) which first led me to think this might just be me. Apparently its not just me

There is s huge push at the end of each year by illicit hijackers so this isn't that big of a surprise. Avast, let us know something if you would please.