I am completely stumped and hopefully someone will be able to give me
some guidance.

Here's our problem:
We are getting an 'NT AUTHORITY\ANONYMOUS LOGON' error randomly when
accessing our database from an asp.net web page. I know that's a vague
description, but it's as good as I can get. We clear the error by
logging off and on the client machine. Here's some of the details of
our setup.

IIS 5.0 Windows 2000 Server (stand alone machine)
SQL Server 2000 SP 4 on a W2K machine (stand alone machine - separate
from IIS)
Client is running XP SP 2.

For the most part everything works fine, but every once in awhile (once
or twice a week), the page throws this error. We have a page that shows
the username on IIS by doing a System.Environment.UserName and it shows
the authenticated user (not anonymous). Our web.config uses
impersonation=true. Now, I am still trying to understand the difference
between System.Environment.UserName and
HttpContext.Current.User.Identity.Name, but that's a different story.
Can anyone help me out? Any would be greatly appreciated.