I've created a 15.10 Ubuntu USB drive and booting off it with an ASUS Rampage IV Black Edition motherboard, I get:
Ignoring BGRT: invalid status 0 (expected 1)
and then nothing. I've become really frustrated trying to get a stable BIOS config with this motherboard (every boot produces an Overclocking failed! message and none of the even low-key default options avoid this message with an i7 3930K - this board rules as the hardest motherboard I have ever configured in the last 10 years!) and now it can't boot a vanilla 15.10 USB drive. I'd really value some help..
I found the solution. See below.