[Zope] login authentication problem

[Finbarr O'Keeffe]

I have changed the security setting on my index_html to only allow
authenticated users to view the page and added the following code to my
homepage zope site (to display the username on the homepage):-
<dtml-var expr="_.SecurityGetUser().getUserName()">

On some PC's this works fine and when you keyin your username and password
the homepage is displayed (with the username shown). On other PCs however
you are prompted to login but once you enter a valid username and password
the homepage is displayed but the username shows as "Anonymous User". Zope
has obviously validated the user but then somehow switched back to
"Anonymous User". I have tried to change various security settings within
the internet explorer browser (version 5) but cannot get it to show the
correct user. Out of 5 PCs, 3 work correctly and 2 show Anonymous User.

Any help would be appreciated

Finbarr