Since upgrading my iMac to Sierra .. and purchasing a new MacBook Pro .. NONE of my memory CF card readers work? I've purchased 4 now and none will be picked up. I've also tried to attached my Nikon D800 by the USB cable and thats not recognised also. Is this a known problem? can someone suggest a CF Card reader that actually works or how to attach my camera with the new Sierra upgrade, Can I go back to the old OS???