[Zope] Why my zope ask me login twice ?

Dear friends on this list, This question probably had been anwsered. But I just search the archie. I add a Ldaplogin Adapter on a folder under my root folder. Then I try to use the ldap to check the user login. When I login the the subfolder. The Zope ask me the password the check with ldap server then ask me again the password again to match the acl_users under root folder. I have no idea. Thanks a lot, Have a nice day Terry