picking object

I want to pick up object in my game. I found this script and I changed the tag to"Pick", but my object dont follow the mouse and this script dont work. What should i do?

 var grabRange: float = 2;    
 var pickPos: Vector3 = Vector3 (0, 0.5, 1.1);    
 var force: float = 30; 
 
 private var pickObj: Transform = null;    
 private var rBody: Rigidbody;    
 private var hadRBody: boolean;    
 private var freezeRot: boolean;
 
 function Update(){    
     if (Input.GetMouseButtonDown(0)){ // if left button pressed...    
         var hit: RaycastHit;    
         var ray = Camera.main.ScreenPointToRay(Input.mousePosition); // create a ray from the mouse pointer
 
         // if object "Pick" clicked, and inside grabRange...    
         if (Physics.Raycast(ray, hit) && hit.transform.tag == "Pick" && hit.distance < grabRange){    
             pickObj = hit.transform; // save the object's transform...    
             pickObj.parent = transform; // child it to the player...    
             rBody = pickObj.rigidbody; // and get its rigidbody, if any
 
             if (rBody){ // if already had a rigidbody...     
                 freezeRot = rBody.freezeRotation; // save its freezeRotation property    
                 hadRBody = true;    
             } else { // if no rigidbody, add one:    
                 rBody = pickObj.gameObject.AddComponent(Rigidbody);    
                 hadRBody = false;    
             }
 
             rBody.freezeRotation =true; // disable physical rotations    
         }    
     }    
     if (Input.GetMouseButtonUp(0) && pickObj){    
         if (hadRBody){ // if already had a rigidbody...    
             rBody.freezeRotation = freezeRot; // restore freezeRotation    
         } else { // if not, destroy the added rigidbody:    
             Destroy(rBody);    
         }
 
         pickObj.parent = null; // unchild the object...    
         pickObj = null; // and signal that's nothing is picked anymore    
     }    
 }
 
  
 
 function FixedUpdate(){    
     if (pickObj){    
         var error = transform.TransformPoint(pickPos) - pickObj.position;    
         rBody.velocity = force * error;
     }    
 }