Firewalls and anti-virus security software are two different creatures -- and generally it's a design flaw when they don't play nicely with each other simply because they are produced by different companies. Avast offers its own firewall -- presumably because it believes its design is better than the default built-in Windows firewall, and users may find it more attractive. The same is true of the Comodo firewall. If one uses Comodo as a firewall and doesn't enable its AV features, and uses Avast as an AV and doesn't enable its firewall features, it is not too much to ask that both companies work to assure their products are compatible with each other. Historically, moreover, Avast AV and Comodo firewall have been compatible, and when they have temporarily failed to be in the past, whichever update caused the problem was subsequently modified. I don't pretend this challenge is easy for companies to achieve, but it is a reasonable user expectation.