I had this happen 3 times on the 8 hour drive back home from Los Angeles yesterday (traffic on the 5 was an F'n NIGHTMARE). It would lock up and not respond to button presses, but kept playing. I had the temp warning off (it got as high as 118F though!). I had it happen one other time while it was on my desk at work but thought nothing of it. Reboots fixed it right up.