Hi and welcome,
first do yourself a favor, remove any personal identification from your posts or sig on the forums. Then what tells you that Avast is interfering with Echolink? you're saying "a" firewall, if you didn't install any yourself, that's Windows firewall and access should be granted when you get alerted about an incoming connection from Echolink >>> it's probaly blocked. So just go to Windows firewall, check if there's already a rule for Echolink there and if it's blocked edit it and allow it. You can also delete this rule and wait until you're prompted again, then allow it from the alert.
You're using Avast free, and it's got no firewall, so it can't block incoming connections. Just to make sure what version of Avast are you running, V4 or V5? also, what's your Operating System?