[Zope] Login fails on all accounts (even init and emergency)

Hi, New user, hope you can help. I've installed zope on a Mandrake 9.0 Linux system. I installed from rpms (Nexedi's, via urpmi). I've tried setting passwords for inituser and for an emergency user via zpasswd (which seemed to go fine). Despite everything, however, when I try to log in to the management interface it gives me a login window, which just won't go away. No matter what username or password I enter, it immediately just responds with a new login window (and hitting cancel simply gives me a "you are not authorized to access this resource" error. Can anyone tell me what I've done wrong? Anything you can tell me greatly appreciated, Marek