HttpContext.Current.User.Identity

Hi, 
We are using Windows Authentication for our asp.net application. The asp.net application is classic, not MVC. We are using HttpContext.Current.User.Identity to get use login name. We are encountering an issue now:
An inner employee in our company just change her last name, and her login is changed from fOldLastName to fNewLastName. We have already changed her login in the active directory. But HttpContext.Current.User.Identity in the program still gives us her old login name of "fOldLastName", not the new login name of "fNewLastName". 
My question is: where does HttpContext.Current.User.Identity get the user's login? Any other ideas about it?
Thanks a lot.



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