I have an EOS 1DMk3 that I purchased second hand many years ago. It will work fine for a while and then throw an Err99. I turn it on and off, I swap batteries, and still, it's Err99. So, I park it for like 6 months, put a newly charged battery in it and then it suddenly works. It will work perfectly for a while. Then it throws Err99 again, but if I keep trying to shoot eventually it starts working again for as long as I use it. When I turn it on again the process of Err99, continual shutter attempts makes it work again. I know the camera is no longer serviced, but I'd like to know if there is anything I'm missing that could make the camera a more reliable shooter? Regards, Tim Murphy
