Hi, I have a battery grip on my 600d and all of the sudden one day it would not turn on. I removed the grip, re-installed the grip and it turned on but ML had an error message on the LCD screen saying the camera was not shut down properly. I've found that if I'm in live view mode and turn the camera off by the switch it won't turn back on. But if I toggle off of live view mode and turn the camera off, everything is ok.