NullReferenceException: Object reference not set to an instance of an object...

I have this code and I do not know how to fix the issue that I am getting. It will let me play my game...but it will not let me take it of pause...so basically I cannot play my game.

 var currentHealth : float = 100;
 var maxHealth : int = 100;
 
 var currentMana : float = 100.0;
 var maxMana : int = 100;
 
 var currentStamina : float = 100.0;
 var maxStamina : int = 100;
 
 var barLength = 0;
 
 private var chMotor : CharacterMotor;
 
 function Start() 
 {
     barLength = Screen.width / 8;
     chMotor = GetComponent (CharacterMotor);
 }
 
 function Update ()
 {
     AdjustCurrentHealth (0);
     AdjustCurrentMana (0);
     
     if(currentMana >= 0)
     {
         currentMana += Time.deltaTime * 2;
     }
     
     if(currentMana >= maxMana)
     {
         currentMana = maxMana;
     }
     
     if(currentMana <= 0)
     {
         currentMana = 0;
     }
     
     if(Input.GetKeyDown("f"))
     {
         AdjustCurrentMana(-20);
     }
     
     var controller : CharacterController = GetComponent(CharacterController);
     
     if(controller.velocity.magnitude > 0 && Input.GetKey(KeyCode.LeftShift))
     {
         currentStamina -= Time.deltaTime * 10;
         chMotor.movement.maxForwardSpeed = 10;
         chMotor.movement.maxSidewaysSpeed = 10;
     }
     else
     {
         chMotor.movement.maxForwardSpeed = 6;
         chMotor.movement.maxForwardSpeed = 6;
     }
     
     if(controller.velocity.magnitude == 0 && (currentStamina >= 0))
     {
         currentStamina += Time.deltaTime * 2;
     }
     
     if(controller.velocity.magnitude > 0 && Input.GetKey(KeyCode.LeftShift) && currentStamina <= 0)
     {
         chMotor.movement.maxForwardSpeed = 6;
         chMotor.movement.mexSidewaysSpeed = 6;
     }
     
     if(currentStamina >= maxStamina)
     {
         currentStamina = maxStamina;
     }
     
     if(currentStamina <= 0)
     {
         currentStamina = 0;
     }
     
 }
 
 function OnGUI()
 {
     GUI.Box(new Rect(5, 30, 40, 20), "HP");
     GUI.Box(new Rect(5, 50, 40, 20), "Mana");
     GUI.Box(new Rect(5, 70, 40, 20), "Stam");
     
     GUI.Box(new Rect(45, 30, barLength, 20), currentHealth.ToString("0") + "/" + maxHealth);
     GUI.Box(new Rect(45, 50, barLength, 20), currentMana.ToString("0") + "/" + maxMana);
     GUI.Box(new Rect(45, 70, barLength, 20), currentStamina.ToString("0") + "/" + maxStamina);
 }
 
 function AdjustCurrentHealth (adj)
 {
     currentHealth += adj;
     
     if(currentHealth >= maxHealth)
     {
         currentHEalth = maxHealth;
     }
     
     if(currentHealth <= 0)
     {
         currentHealth = 0;
     }
 }
 
 function AdjustCurrentMana (adj)
 {
     currentMana += adj;
 }