Might be a session/login issue with the site.
If you're logged in to the forum it is possible to not be logged in to
the 'site' (check for the 'your details' link in the top-right). You
must be logged in to both in order to access the Chat at the moment.
I'll look into the code and see if I can make it simpler - at some
point I'll be modifying the login to the site so that it stays logged
in just as the forum does.
(I also remember we had similar problems before when the chat was
running and it was one of the reasons I pulled the link for it - ah
well can't win 'em all).
Thanx for letting me know.