set a new camera target from another game objects script

i´ve got 2 scripts, one for the camera movement and one wich controls the selection of the gameObjects in my scene. The selection script is attached to every selectable Object, the Camerascript on the camera... What i want to do now is when i´m selecting a gameObject i want this to be the new Camera Target. Unfortunatly now when i try this the selected GameObject is not set as an Instance of an Object in the Camera Script. Hope you understand my problem. Here is the some script of the Selection:

     meinscript = MyGUI();
     var mausscript : Mouse = gameObject.GetComponent(Mouse);
     if (GUI.Button (Rect (6,90,100,20), "Set as Center")){ 
     mausscript.test("GameObject1");
  }

Here is some Code of the CameraScript:

 function Start () {
 test("GameObject"); // to select a GameObject when i start the game (works fine)
 }
 function LateUpdate () {
    
         x += Input.GetAxis("Mouse X") * distance *2;
 
         y -= Input.GetAxis("Mouse Y") *2;    
 
         y = ClampAngle(y, 1, yMaxLimit);
 
         var rotation = Quaternion.Slerp(transform.localRotation,Quaternion.Euler(y, x, 0),Time.deltaTime*10/2);
     var position = rotation * Vector3(0.0, 0.0, -p) + mytarget.position;
 
         transform.rotation = rotation;
 
         transform.position = position;
 
 } 
 function changeTarget(giventarget:Transform){
         mytarget = giventarget;
 
 }
 //this is the function wich recives the name of the GameObject wich should be the new camera target
     function test(targetbrick:String)
 {
     var testtarget = GameObject.Find(targetbrick).transform;
     changeTarget(testtarget);
 
 }

Now when i try to change the target from the selection script this is the error message i get: NullReferenceException: Object reference not set to an instance of an object