There is a known bug when using RobotC with crystals. When playing a competition plugged into a field controller, the robot will time out 2 or 3 seconds to early. This has been tested with RobotC versions 1.4 and 2.0.1. To fix the problem, replace

#pragma userControlDuration(120)

with

#pragma userControlDuration(255)

The robot will still stop at the end of the game, as the field controler will disable the transmitter.

This is only for crystals. VEXnet does not have this problem and you can remove the user control duration and autonomous duration lines altogether