gives a good explanation of what is happening and how to work around it in Reply #1 below.

I recommend having various different cards with the boot flag set because soon we'll be running something that might not work on certain cards or might corrupt the file system. You can also set the card boot flag using a utility like EOScard for Windows and for Mac try MacBoot. You should install ML on a few cards if for nothing else so you'll have cards with the boot flag set. You'll find the ROM dumps in the ML/LOGS directory of the card. This is necessary in order to get firmware dumps, set the camera boot flag and to set the boot flag on the memory cards that you'll be using. OK-first step is getting ML working on your camera with the supported firmware. Major updates that add new features or porting to a new camera isn't covered here. Note that this article is about doing a relatively minor firmware update like the type Canon released around October of 2016 to fix a problem that affected a couple of lenses. There are several ways to do this and there are plenty of tutorials for compiling ML so we won't go into it here. The first thing you need is to set up a development system in order to compile Magic Lantern. You don't need to know anything about programming or reverse engineering and quite frankly most of what is required to do is grunt work that the main developers aren't really interested in doing. Let's put the emphasis on you can meaning anyone reading this article should be able to port ML to a Canon firmware update, though it probably shouldn't the first project you attempt. Canon may have actually fixed a bug that affects your camera.The old firmware that ML needs is no longer on the Canon support site so you'll have to get it from a non-official source.Canon recommends using their latest firmware update.However, there are also reasons for porting to the latest Canon firmware: Because you need a degree in computer science, know ARM processing and spend hundreds of hours reverse engineering to port Magic Lantern.Developers shouldn't waste their time on trivial updates.

If ML works on X.X.X why take a chance on breaking it?.

There's nothing in the firmware update that you really need.

Pretty much every week someone posts something like, 'When is Magic Lantern going to be working with X.X.X version firmware?' The answer is usually, 'Downgrade to X.X.X -1.' Why doesn't ML work with the latest Canon firmware? There are reasons including:

Updateing canon 7d firmware