Getting current user name

I am at the start of building a company intranet.  I have published the master page, default page and a couple of simple pages to our IIS server.  Because this is an intranet, I am using Windows Form authentication.  In the default.aspx page's load, I am trying to set a variable to the current user's logged in ID.  This works on my local development machine, but when I publish the site to the IIS server, it does not.  In the page load event, I have HttpContext.Current.User.Identity.Name to get the current user logged in.  Is this not correct?
Thanks for the information.
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