Hi,
Please go to /System/Library/CoreServices/ and launch the Expansion Slot Utility. Ensure that the second PCI Profile has been chosen, ie x16 Lane Graphics Slot + Two x4 Lane and One x1 Lane Slots. Also ensure that the Multibridge Pro is connected to the top slot, ie slot 4 in your Mac Pro. Finally, ensure you have the Multibridge 6.1 drivers installed. This should ensure that all works well but, if it doesn’t, then please double-check that the PCI Express cable is firmly connected to both the adatper card in the Mac Pro as well as the Multibridge box itself. If the thumb-screws are loose, the Mac Pro may fail to see the Multibridge. If none of this works, then please contact your reseller for a replacement unit.
Regards,
Luke Maslen
Blackmagic Design