Hello Tech. My info is in my Sig line. I update my Vista Basic Home, Avast, and CA Firewall every 2-3 days at the longest. All were updated last night around 4am. EST USA.
Sorry, I have, generally, hidden signatures on forums

Maybe some bad interaction between avast and your firewall.
Maybe you can activate logging in WebShield:
1. Edit <avast>\data\avast4.ini file
2. Find the section [WebScanner]
3. Add the line:
EnableLogging=1
4. Restart Web Shield in XP/Vista (terminate and start again)
5. Browse (trying to access some webpages)
The log file are <avast>\data\log\ashwebsv.log and ashwebsv.ws.
They would be accessible when WebShield is terminated again.
Post them here or send by mail to rypacek (at) asw.cz
After that, disable the logging to avoid a big log file.