[Zope] ZMI Help System

Hi there A strange one here : i cannot access some part of ZMI HELP system. running Zope 2.7 i got to the manage part of the site using my admin login and password. then when i try to access let say "Caching Policies Tool Interface" under API Reference i have a pop-up asking for authentication again. Trying to put in same admin login and password fails ... Something stupid i am missing here ? Thanx in advance seb Note : it is not a fresh database i ve upgraded from 2.6.2