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And that could mean it won't know how to install another firmware image. Firmware is what the devices uses to figure out how to do things like powering up, so messing it up can brick a device if it's not installed correctly or only partially installed.
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ML runs on top of the firmware (hence the requirement for a specific version) and needs to be installed after the firmware update. I'd also make sure you've cleanly uninstalled Magic Lantern from the 1100D via the ML format command (DO NOT JUST DELETE THE FILES!), if you've somehow managed to install it (hopefully you haven't).
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I would personally format the card that has 1.0.6 on it (since you can download that from Canon, you may not need to archive it, unless you're paranoid they're going to get rid of it), and put v1.0.5 on it for firmware upgrading. zip file also has a PDF in it with instructions on how to copy it to the memory card and then run firmware updating on the camera. zip of the FIR file for v1.0.5 is listed right there on the Magic Lantern website.
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