I'm also having this problem right after installing 11.1.2. Frequently getting MEMORY_MANAGEMENT bsod's on my Windows 8.1 guest OS, sometimes right at startup, sometimes a few minutes after logging in. I have no "Advanced Options" link available in my config, so no "Nested Virtualization" option to disable. Going to try and reinstall 11.1.1 from the link posted earlier. Not a great morning! Also disappointed to see other people reporting this earlier in the week, but I was still prompted to install this "update" days later on Friday. Shouldn't this have been pulled?