It could be a few things. Just a couple of questions...
When you type /join #pokebeach.com, what does Chanserv respond with? Usually the problem is right there. If you're using mIRC, you can find all of that info in the 'DejaToons KingdraKing' section.
You're sure you've done nothing to be banned from the chat?
EDIT: You were banned, apparently for spamming... Whoever banned you has taken it down, though, so you should be able to get back in.