Well, that server works fine, and I can successfully join a channel, so..
If you can't join a channel, there will be an error message of some description. It should be in the status window for the server, but if you are running a script of some description, it could be anywhere.
Are you on other servers at the same time? Are you running a script? Is the 'join' command re-aliased (//echo -a $isalias(join)) ?
