Compatibilty issue

I doubt that its a compatibility issue. I have the same exact mobo and I find that its hard to add new cards, memory to it. It possible that the issue you are having is that the PCIe slot is dirty and/or faulty. In my mobo its the DIMM slots that won't accept new RAM but it will read the old one if I flex the mobo a bit. If I don't flex the mobo even removing and putting back the old RAM will cause the mobo to not recognize that there is RAM installed. Its really a sucky mobo imo