FPSController doesn't climb ladders

I've been trying to make the FPSController (the one that comes within unity) capable of climbing ladders. I've used this script that I saw in the forums and attached it to the ladder:

 #pragma strict
 
 var playerObject : GameObject;
 var canClimb = false;
 var speed : float = 1;
 
 function Start ()
 {
     playerObject = gameObject.Find("FPSController");
 }
 
 function OnTriggerEnter (collider : Collider)
     {
         if(collider.gameObject == playerObject)
         {
             canClimb = true;
             playerObject.rigidbody.useGravity = false;
         }
     }
 
     function OnTriggerExit (collider : Collider)
         {
             if(collider.gameObject == playerObject)
             {
                 canClimb = false;
                 playerObject.rigidbody.useGravity = true;
             }
         }
 
         function Update ()
         {
             if(canClimb == true)
             {
                 if(Input.GetKey(KeyCode.W))
                 {
                     playerObject.transform.Translate (Vector3(0,1,0) * Time.deltaTime*speed);
                 
                 }
                
                 if(Input.GetKey(KeyCode.S))
                 
                 {
                     playerObject.transform.Translate (Vector3(0,-1,0) * Time.deltaTime*speed);
                 }
             }
         }
          

The variable that makes sure that the player is in range works and in fact the "useGravity" variable of the rigidbody unchecks but the character is still not able to climb the ladder. I'm new to Unity I can't figure out what's the problem.