Did you get a 5D2 or a 5D3?
If you have a 5D2, I believe you can run the latest firmware with ML on there. If you have a 5D3 you have to run firmware 1.1.3 (not the newer 1.2.1).
I would check the Magic Lantern website for more information regarding your particular setup.
°°°°°°And remember – Magic Lantern is a hack and is therefore not responsible for camera malfunctioning, breaking, or any warranty that may be voided. You are altering the cameras software in unauthorized ways. If anything goes wrong Canon will not help you out. Just be aware of what you’re doing.********
Ryan Holmes
http://www.ryanholmes.me
@CutColorPost