Can you activate logging in WebShield?
0. (Disable avast self-defense module: Program settings > Troubleshooting tab of settings.)
1. Edit <avast>\data\avast4.ini file with Notepad (or use step 0 with other text editors).
2. Find the section [WebScanner]
3. Add the line:
EnableLogging=1
4. Restart Web Shield in XP\Vista (terminate and start again) or whole PC in case of Win98
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.
Oh, enable the self-defense module again after that if you have to follow step 0.