Double-hop to database server fails if user does not logoff every

I have a problem with asp.net 1.1 web applications on IIS 6.0 that work
fine unless the user has not logged off and back on to the network every few
days.

The web applications are using a double-hop to pass the current user
credential to the IIS web server and from the web server to the database
server (SQL Server 2000).

When the problem occurs all the user does to fix the problem is log off
the computer and log back on. The web application then works for a few days
until it starts to have a problem again. Locking the computer and login in
does not fix the problem. Also the web application is not left open for the
period of time and when the problem occurs exiting IE and reopening the web
application does not fix the problem.

I suspect the problem has something to do with the loss of or coruption of
the Kerberos credentials.

Any idea?

Because this crosses several technologies I am not sure where the best place
to post this question. I am open to suggestion on a better or additional
places to post this question.
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Mark