Thanks Marc - I assume that because there IS an error code, then the techies will know what to do. Just wondered if it was a recognised problem and whether other users had experienced the problem. The camera just hangs with the egg timer icon permanent and 'starting up' showing in the viewfinder. it seemed to be exaggerated using the image bank and the back stayed powered up when image bank was removed.
Updating to V4.8.3 didn't cure it and then the camera, back and viewfinder just lost contact with each other. Multiple tries of removing the viewfinder, back and lens in different order eventually got me up and running again. I also had to revert to original firmware, which, thankfully I had kept on my laptop. ( I was on a shoot at the time ).
I am using an H3D39 II in the meantime. I like the benefit of the larger screen. Happy to have a chat, off the forum, if you are interested in knowing what happened.