joanlui,
If you were using Kerio 4.0, I can understand the problem. For some reason, Kerio 4.0 is not as stable as the older 2.15 version. It is a very good firewall.
Outpost is a reliable firewall which I have tried in the past, but settled for Sygate instead.
Another good FW is Tiny Personal Firewall, however the learning curve is high.
Stick with Outpost if it is working for you and does not cause any conflict with AVAST. It shouldn't.
Good luck,
techie