Windows... two cards on board, one on riser. Whichever card on board isn't plugged into monitor, gets "Sick"
Install trixx and check in settings> Disable ULPS
that should do it.
make sure your motherboard likes the risers!, I have an ASUS M4N75TD that refuses to work with pcie risers at all, all of my other motherboards has no problem, but this one has a serious attitude!