Well, phazenet won't connect here using port 7000 either, so that's a port issue on that network (or a server on that network). The others I can connect to using those specific ports. You might try specifying different ports and see if you find any that work for one of those networks.
For example:
/server irc.afternet.org 6667
Just replace the port with another common port and see if any work for you on that one network. Beyond that, since you have the firewall off, it could be your router settings or your ISP trying to block IRC but not doing a complete job of it.
