I'm aware you don't want to connect to freenode, but the point of the exercise was to rule out your specific server as the culprit, so without actually testing a connection to a known working server you can't really say this is mIRC's fault.
If the antivirus blocking ports is what's causing the problem, reverting to 6.21 will likely *not* solve it. Disable both your AV and windows firewall completely (again, to *test*) and try to connect. If the connection succeeds then you know what to fix. Sorry, we can't help you configure your AV, you'll have to look what one up from whatever vendor makes the software. As far as your windows firewall goes, there should be an allow for 6667
Finally, like i mentioned above, you must verify that the port you're connecting to is indeed allowed by your AV/firewall.
The best way to do this is to type /server irc.freenode.net 6667 and test if it works.
