I'm using MSI cards. I'm not sure if that makes a difference. Also I heard that the card has to be attached directly to the motherboard. No riser.
Thanks alot! The point was to put it directly in the motherboard. That worked for me (Gigabyte card).
Looks like the bios identifies if the card is in a PCI 1x or PCI 16x slot - somehow this makes a difference.
Glad to hear you got it working.