[Zope-CMF] Plone security?

[David Forslund]

I'm fairly new at running plone, but I really don't understand the 
security model.   I have added some folders and documents, but for
some of them, another user gets a popup window asking for a login
(after they are logged in) to see the document.   This doesn't accept
any users password.  It only happens on some files or documents.  I 
don't understand what is going on.  I've done some editing on users
permissions, but I can't tell what is causing this.

Also, I can get to the site as a user, but that user isn't listed
as one of the users. I can register as that user, but now there appears
to be the same user in two different places, but I don't think they are
the same.

Dave