Does this happen only for this server? Try
rumble.dal.net or even
irc.dal.net as well. Even try other networks such as
irc.undernet.org,
us.undernet.org,
eu.undernet.org,
irc.efnet.net, etc. Also try the regular 6667 port, rather than 6666.
In future it'll probably be best to remember to post any questions relating to issues with connecting in the
Connection Issues forum