Hi Claus,
please see SAP Note 1732610 (SPNego ABAP: Troubleshooting Note). Section 2.2 (2.2 Flow ends here with a page reading alike "Your browser is not configured for using SPNego" (see flow step 2))
If this does not help a more detailed kernel trace should show the details of this error message. See section 3.2 on how to get such a kernel trace.
Regards,
Mathias