I click on an entry and it becomes highlited. I select clear log and it looks like something took place but if you scroll back you will find your entry is still there. ???
If you mean Scan Computer > Scan Logs > Delete Log …it works here
EDIT: sorry you mean Firewall log…my bad…
if i mark everything in the log and click clear log i get AvastUI.exe crash ???
…stupid firewall log
5.1 is supposed to fix this.
Links to other posts on firewall log problem
http://forum.avast.com/index.php?topic=59421.0
http://forum.avast.com/index.php?topic=58495.0
its going to be fixed in the next program update