[kjohnson]

If you are using tank drive, make sure your joysticks are ordered correctly on Setup tab of the Driver Station. Typically the left is Joystick 1 and the right is Joystick 2. With the robot disabled, click the trigger on one of the joysticks and you should see green asterisks display in the list. If you need to swap the joysticks, simply click and drag them into the right order.

If your joysticks are already in the right order or you're using arcade drive, check your PWM setup like Bill mentioned above.