Need Help with Page.User.Identity.Name

HelloLabel.Text = Page.User.Identity.Name
I have the above statement in the Page_Load sub on the masterpage.  When I run "Start Debugging" from VS 2008 it works fine.  However, when I publish the Web Site (on the same machine) and try to load the site from our internal network, the information is blank.  Can someone point me in the right direction please :P 
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