I was in the mountains a few weeks ago and flew in the morning. It was 35F. I had done a cold IMU calibration a few months ago and normally the Phantom starts right up. This time I got an undefined error but then it went away after 30 seconds or so. The Phantom had me wait about 30 seconds to warm up. It then flew just fine. I suspect that the undefined error might have been due to the altitude (around 9000 feet) and the cold.
Also, you NEED to be wearing gloves! My hands got so cold I had a hard time keeping them on the controller.