I have applied 4.6.623 this morning, and I too could not load any pages.
I applied the patch as detailed on another thread, but having re-booted I still have the same problem.
It seems that if I stop the Webshield (via the Avast Interface) and then re-start it all seems OK, but I wonder if it is actually running after the re-start:w ith the Webshield indicating it is running I do not see the "Scanned count" doing anything other than showing 0 files. Additionally, with the "Show detailed info on performed action" button ticked it is no longer telling me what it is doing on screen.
Just noticed that it has "The provider is waiting for a subsystem to start" at the top of the screen. I don't know what it is waiting for.
Win XP, SP2, patched up to date.
No additional firewalls.