We had our stop button die on use during the competition. It had happened once or twice during testing, but went away after a reboot so we figured it was a code issue.
After some probing with the multimeter, it turns out that we had a busted connector on the end of the stop button USB cable. The ground connector was losing contact intermittently. A quick run to Wal-Mart Friday night (snuck past the manager 5 minutes after closing
), and some soldering Saturday morning, and we had spliced in a new connector on. That solved the problem for the weekend.
If you open up the stop button, they are very cheaply made. There is a piece of kite string in the cable that serves to give it tensile strength. Our had solder balls and burned bits on the board. I think I'll open it up tonight and clean it out now that I'm home and have a good soldering station.