@ Prophet
As you can see from my signature I use Outpost Firewall Pro 7.0.4 no problems with it and avast. You don't say what version of Outpost you are using and this is essential ?
However, when you install Outpost (depends on which version) it should detect that you have avast installed and it will ask you about a compatibility install, e.g. not installing its web control or anti-spyware as avast has both of those functions covered (and much better too). So did this happen and what did you answer ?
So which was installed first ?
If you already had Outpost installed, I don't know if it throws up the compatibility question, so I would suggest that you export your configuration settings so you have a copy that can be imported later.
Uninstall Outpost, reboot, install avast if not still installed. Reinstall Outpost and answer yes to the compatibility question so it doesn't install the web control or anti-spyware modules (you could of course do a custom install excluding those modules). Import your saved configuration file settings and reboot.
@ mangudix
You can answer the same questions too please.