From Roko:
Did you have ZoneAlarm installed at any time and uninstalled it?
I had problems like yours with Web Shield. I tried it all and all failed. Then I found that one file from ZoneAlarm was still on my PC after uninstalling it more than a year ago. So if you had ZoneAlarm and uninstalled it, try if the file "vsdatant.sys" is still on your PC. If so, boot XP in save mode and delete the sucker. It solved all my problems, no kidding.
Now that you mention it, I do remember uninstalling Norton Antivirus 2002 (v8.something-something, can't remember) several days ago just before installing Avast!. Since then, Spybot S&D has been giving me registry change alerts from its TeaTimer resident task about four registry changes that are always being deleted at startup which are related to NAV 2k2. These four values are always the same and are always being deleted at startup as I always allow Spybot to allow this to happen. I'm still trying to find a way to get rid of whatever it is that's causing this, but have found no success so far.
Here are the values that always delete at startup (as recorded from Spybot's TeaTimer records):
"NAV Agent" (new data: "") deleted in System Startup global entry!
"Symantec NetDriver Monitor" (new data: "") deleted in System Startup global entry!
"ScriptBlocking" (new data: "") deleted in System Startup global entry!
"{42CDD1BF-3FFB-4238-8AD1-7859DF00B1D6}" (new data: "") deleted in Global browser toolbar!
Would anyone know what's causing this to happen?
Fricken' Symantec......