Andreas,
Try this:
1. Go to GPIB under Control panel
2. Select GPIB interfaes one by one (i.e, GPIB0, GPIB1 etc) and then select board type as 'None'
3. Then close the GPIB configuration and reboot the machine
4. Go to GPIB under Control panel again and pick PCI-GPIB from the list. Exit again and it should be able to save the changes.
Nasir