system.web.httpcontext.current.user.identity.name shows old usenam

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We changed a username in AD. The user now logs on to a computer on our
network using the new username without any problems. They can not logon using
the old username. However, when they access a IIS 6.0 web site where a
programmer compares system.web.httpcontext.current.user.identity.name to a
lookup table containing usernames they could not gain access with the new
userid. We created a web page to show what
system.web.httpcontext.current.user.identity.name is returning. It is
returning their old username. If we put the old username in the table the
user may access the web site. The IIS site logs for the web site show the
new username for the user as he accesses the site. I have used adsiedit to
look at the user's information in AD. It shows only the new username through
out the the account parameters.

We also have a sharepoint 3.0 site that shows the user's old username when
he accesses that site.

What can I do so system.web.httpcontext.current.user.identity.name will
contain the new username for this renamed account?

Thank you,
Antonio