HTTP Error 401.1

[k3lvin]

We have are having authentication issues with our intranet server. Some users are getting the following message when they try to access some of our internal websites. "HTTP Error 401.1 - Unauthorized: Access is denied due to
invalid credentials" We have determined that it has nothing to do with the version of IE as the error happens on 6, 7 and 8. Or the user account because the user can log onto a different computer and everything works. I get the same error when using the domains admin account too. Also get this issue on a new install of Windows.

This must be a server issue rather than a client issue. I keep getting these Kerberos errors on our domain server which must be part of the problem:

A Kerberos Error Message was received:
on logon session
Client Time:
Server Time: 10:16:45.0000 11/2/2009 Z
Error Code: 0xd KDC_ERR_BADOPTION
Extended Error: 0xc00000bb KLIN(0)


A Kerberos Error Message was received:
on logon session
Client Time:
Server Time: 10:13:49.0000 11/2/2009 Z
Error Code: 0x7 KDC_ERR_S_PRINCIPAL_UNKNOWN
Extended Error:

I am really stuck, has anybody seen this before? Any help will be great. Thanks.

Intranet server: Windows Server 2003 and IIS 6.0
Domain server: Windows Server 2003 IIS 6.0
Client computers: Windows XP Professional and Internet Explorer