this article may have nothing to do with your situation but...
XADM: Error Message "Error 500: Internal Server Error" Browsing Public Folders
SYMPTOMS
If you use a Web browser to gain access to Microsoft Outlook Web Access (OWA) and browse the public folder tree of Exchange 2000 Server, you may receive the following error message from the Internet Information Service (IIS):
Error 500: Internal server error.
You cannot navigate further through the public folder tree.
Also, when you view a frameset page (for example, OWA), one or more panes of the frameset may display properly but the remainder of panes may not.
CAUSE
This issue can occur if Kerberos authentication does not work between the client (the Web browser) and the IISthat hosts the public folder tree because the time on the client computer is more than five minutes out of synchronization with the server.
RESOLUTION
To resolve this issue, synchronize the time on the client computer with the time on the server computer.
WORKAROUND
To work around this issue, increase the length of time that Kerberos authentication allows clients to be out of synchronization with servers by modifying the default domain policy. However, if you modify this default, you may increase the security risk of a client with a time that is out of synchronization.
In default domain policy, open the following sections: Windows Settings, Security Settings, Account Policies, Kerberos Policy. Modify the Maximum tolerance for computer clock synchronization setting.
MORE INFORMATION
see the "Windows 2000 Kerberos Authentication" white paper from the following Microsoft Web site:
http://www.microsoft.com/windows2000/library/howitworks/security/kerberos.asp
regards, lazarus.
