A new cause for Error 30, perhaps? This happened about three times on Saturday with my 7D with OEM grip. When I got home I tried switching batteries, lenses, etc., and the problem only got more frequent. It got to the point where I could take one shot, and the next one would fail, creating a black image. I would then have to remove the batteries in order to take another shot. Finally I took the grip off, and have had no problems since.
Of all the possibilities, a failed grip is the least troubling, given that I need this camera to be working this coming weekend.