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Isn't that what the lightning bolt signal in the viewfinder is supposed to indicate?
FWIW, I have a 580EX version 1 and the connection between it and my 1DIIIs and 1DIV has gone flaky as well, where either the flash doesn't fire, or loses ETTL. More so with the IV, yet both cameras work fine with radio slaves in the hot shoe (most of the time). Just picked up a 1DX and it has worked perfectly with the 580, but of course, this has only been test situations and not real world assignment shooting... Anyway, my point is part of the problem could also be the camera's hot shoe somehow losing connectivity over time, maybe from working slightly loose, or something, where the weight of the 580 'triggers' the problem and lightweight radio slaves, or smaller flashes don't... Not sure....