In a Domain with GPO security restrictions in place, specific group policy settings change with the installation of Windows Server 2003 SP1 and can cause this problem. If you have followed and implemented the recommendations in the Windows Server 2003 Security guide, you may have configured the 'Network Access: Named pipes that can be accessed anonymously' and set this to a blank value. This GPO setting makes changes to the registry key HKLM\System\CurrentControlSet\Services\LanManServer\Parameters\NullSessionPipes. On a domain controller running Windows Server 2003 without SP1, the default values are COMNAP, COMNODE, SQL\QUERY, SPOOLSS, LLSRPC, EPMAPPER, LOCATOR, TrkWks, TrkSvr but these values change when Windows Server 2003 SP1 is installed to include COMNAP, COMNODE, SQL\QUERY, SPOOLSS, LLSRPC, BROWSER, NETLOGON, Lsarpc, samr.
If your existing GPO setting value is set to blank for the setting 'Network Access: Named pipes that can be accessed anonymously' and Windows Server 2003 SP1 is applied, when you view the value of the registry key or run a RSOP in GPMC, the value will appear blank however when you open the GPO and view the setting, it appears with all of the new Windows Server 2003 default settings: COMNAP, COMNODE, SQL\QUERY, SPOOLSS, LLSRPC, BROWSER, NETLOGON, Lsarpc, samr.