'Connection refused' is a common error - there have been lots 'n lots of threads about it, use the Search feature, expand to 'All Forums' and 'All Posts' for best results.

It's worth noting that Rizon have been having some DNS issues recently, perhaps that's related?

Also try:
  • Disabling the Windows XP Firewall (Service Pack 1: www.mirc.org/xpdcc | Service Pack 2: www.mirc.org/xpdccsp2)
  • Connecting to a different port (try 6667, 6668, 7000)
  • Try an individual server address. Check www.rizon.net for a list of servers.
  • Disabling antiviruses and other 3rd party firewalls, and then restarting mIRC. (disable them only temporarily)
  • Try /dns server.name.here and connect to the IP of the server.
  • Try other IRC networks to see if it's specific to Rizon, or if it's your end that is the issue. For example, /server irc.quakenet.org.
  • If all else fails, close all other 3rd party programs to make sure it is no interference from them - MSN Messenger, Kazaa, all of it.