Menu doesn't expand

I got a problem with a site i'm setting up. There are two slighlty different navigations for two different roles. The second navigation has only a few more parents than the first one, so the navigation look quite similar. The first (initial) navigation, which is only displayed for some user,works fine. The second navigation, which is only displayed for some other users, doesn't work although it's almost the same. None of the parent menus does expand by clicking them. If I set the menu to Always expand, it works fine, but that's not the way I want it. How can I get the second navigation to work?