* Put your robot on blocks so it wont drive.
* Add print statements to your code that lists the distance and motor output value for each loop itteration.
* Run your code while moving an object in front of the ultrasonic sensor.
There's got to be a case where your if/else logic doesn't result in the motor.drive() method being called.
Also, why are you using the setSensitiviy method, that affects turning not rate of travel.
See:
http://team2168.org/javadoc/edu/wpi/...obotDrive.html