I have been getting this error for several weeks - since I first starting using Avast. It's random for me though. Maybe happens once an hour or so and it happens on ALL sites, but my email still works, so I know there is a connection still. To enable my web browsing again, I have to go to Avast Shields Control and I disable ALL shields for 10 minutes. Once I do that, IMMEDIATELY all web browsing works again, for about an hour or so when it does it again.
It's a bit frustrating!