[Zope] problem accessing object as anonymous

[robert rottermann]

Hi there,
I try to find out, why  in an intranet accessing an object from a link sendt by
email is not possible.
situation:
a user from a plone intranet sends a link to a dokument within the intranet to a
colleague.
if that colleague clicks on the link while *not logged* into the intranet she is
presented with the *browser* login box repeatedly. entering the credential does
not help.
the error log shows that access to the document is forbidden for the document
for the user Anonymous

while debugging I found out, that the __roles__ property of a given document is
a tuple of the form
('GroupMember', 'Guest', 'Manager', 'FolderManager', 'Owner')

if I copy the same document to a vanilla plone site its __roles__ property is
['Anonymous', 'Manager', 'Reviewer', 'Manager', 'Anonymous']


I have the impression, that when 'Anonymous' is part of __roles__, access to the
object is possible. without it, access fails.

now my questions:
is the assumption, that the failed acces is caused by the missing 'Anonymous'
role in __roles__ correct?

if yes: what controls the setting of __roles__

if not: what could be the reason of the fact, that users are not presented the
cookieCrumbler-base plone login is not presented?

thanks very much for your help
robert