Actually try this, I think it's better than turning your web shield off.
I followed this suggestion found on this thread: http://forum.avast.com/index.php?topic=120600.0
, and had the issue fixed. Do this:
avast! GUI -> Security -> Web Shield -> Settings -> Main Settings
Enable: Scan traffic from well-known browser processes only
Enabling this doesn't make avast! any less secure from what I've read.