[Al Skierkiewicz]

Evan,
That seems to be the case in most lockups according to the CSAs. It also depends on the batteries you use for the NXT. If you are using the standard single cell battery pack, the terminals sometimes need to be realigned. In the heat of battle, they become deformed and do not hold a tight connection in motion. It is similar for the rechargeable packs but they don't seem to be as critical. Remember that there is always other issues in the way you write your code as well. I am not an expert in this part so take this with a grain of salt. If your program is waiting for input from a sensor that has become disconnected or is intermittent, then you may experience unpredictable results. In that case, the software is running but it is merely waiting for an expected input that never comes.