But also it could be the way you sign in.. I believe you have to sign in again when you go to the chat area. There is a button for 'login' and if you want to access chat i think you have to do that, even if you are already signed in to the boards.
What specifically is happening when you try to log in? do you get in but then can't post anything? Or when you try to post it says you're not logged in?
I don't know how macs work with this chat software here..