It's using ajax calls to content/treemenu/<id> to get the content of the containers, use firebug to see if the call is: 1. done, 2. taht it is not blocked (http: 200 OK) and 3 the response of the call.
If 1 fails, then I don't know, if 2 fails, then it is most likely rewrite rules for index_treemenu.php that fails, if 3 fails, then the repsonse should give you a hint.