the short answer is that desktop/gaming cards aren't supported in thinkstation systems. you could try freeing up some ROM space in the BIOS by disabling unused devices, but there's no guarantee this will work. lenovo doesn't support non-workstation graphics cards so it's up to the end-user to find a solution in such cases or revert to a supported workstation card.
but, try disabling devices and see if that helps. it's certainly worth a try.