I was on a shoot this past weekend and the moment that every photographer fears occurred: the camera stopped working. I got an error message saying "Camera Error Turn power off then on." No matter what I did, I couldn't get into the menu or get the camera to take a photo, nothing.
Granted, it was about 100 degrees outside. If my camera had stopped working because of the heat, I'm not sure I would have blamed it. It was freaking hot. But I still needed a working camera, so I got online and tried to research the issue. I didn't find much besides, "take the battery out," which feels like the camera equivalent of the Nintendo 64's "just take the game out and blow on it." Needless to say, nothing worked.
The problem stems from the IBIS. Some said if you take off a lens while the camera is on, this will occur. That would be an unusual thing for me to do, but I suppose it's possible. I tried all sorts of reversing the process with taking the lens off and putting it back on, but that didn't help. Neither did sifting through forums and herds of internet trolls.
Anyway, here's the solution: Turn your camera off and on in rapid succession 3 or 4 times before the menu pops up.
This should somehow reinstate (or throw off) the IBIS to make it function again. But even after it started working, if I turned my camera off it happened all over again. So I just had to repeat the solution.
The shoot ended and thankfully I was able to fix the problem and finish the shoot. By the time I got home, the camera wasn't having the issue anymore. So it's possible it could have been a combination of the heat and IBIS, not sure. Either way, having a backup camera handy is always a good idea.
One more thing: I saw someone mention that this was a firmware issue of the A7ii, v. 1.10. I've tried to upgrade but it wasn't succesful, so I can't confirm that or not, but something to try. Hope this helps you out in a bind!