If you are trying to connect to irc.mibbit.net and you are banned with a notice similar to this,
Sindacious[127.0.0.1] (User has been banned from Mibbit ((127.0.0.1) was found blacklisted (DNSBL)))
Then you're connecting to the network with a blacklisted IP address.
Where to request for removal
When you're banned form the network you will get a notice looking something like this:
(IP_ADDR) was found blacklisted, see http://njabl.org/cgi-bin/lookup.cgi?query=IP_ADDR
When banned, go to the link that is provided in your ban message, then request for removal after looking up the IP address and seeing the reason why.