I can partially confirm what PhDminer was talking about earlier with the low temperatures. I took a unit offline to do a firmware update and after letting it sit for a couple minutes I had a hell of a time restarting it. It is a good performing (39GH/s @ 1.1V) unit, but it kept on restarting while it was powering up as it never got time to warm up. I ended up getting it started by removing the fan blowing cold air on it (it's -29C outside right now) and letting it get started and warmed up. I'll have to look into it deeper in the next couple days why it's doing this.