I have a Lumenier DX600 DVR which is normally a really nice piece of kit, and even has it own screen. However, a couple of times in my last 4 or 5 flight when I have gone to look at it and turn it off after the flight and it has been locked up - frozen screen, and not responding to any of the switches. On rebooting the video files are there but of unrecognised format - i.e. unplayable. I wondered if anyone else had ever come across this, and whether there is something which may be triggering it. I wondered about changing the SD card to a different brand, but I am clutching at straws. Any suggestions ?