Iv'e just put my new IQ4 on the XF body for the first time and the shutter will not release using the camera button or the button on the IQ4 screen. Mirror-up is unresponsive as well. Firmware is the latest release and I've reset the camera controls to default. My old IQ3 back works without issue so that rules out a mechanical issue with the body. I know Capture Integration tested it before it shipped and I can see 18 frames on it, so it must have worked at some point. Anyone out there experienced this problem?