that IP is the SantaAna.ca.us.undernet.org server, however that error appears to be an issue with the mibbit client, and/or the IP you are connecting to that undernet server with, anyway, try the following:
1. Try a different undernet server.
2. Ask the creators of mibbit
3. Try to contact the server admins (email@example.com
with the ip you are trying to connect from is a good place to start, incase it is a g-line issue, otherwise they will be able to advise you who to contact regarding the specific server).
As mibbit is not a client/service controlled by Undernet, it's creators are probably the best people to talk to first, as there doesn't appear to be any issue with the undernet server in question or Undernet in general. :/