Translating from game space to view space

I'm trying to overlay a gui element onto the gameobject this script is attached to. But I keep getting an error that states :

 Assets/flashing_script.js(16,19): BCE0023: No appropriate version of 'UnityEngine.GUI.Label' for the argument list '(UnityEngine.Rect, float)' was found.

Any help would be wonderful. I'm pretty much a noob at this :).

 var timer : float = 3;
 
 var viewportPos : Vector3;
 
 
 function Update () {
     
 
         viewportPos = Camera.main.WorldToViewportPoint(transform.position);
     
 }
 
 function OnGUI () 
 {
             
     GUI.Label (Rect (viewportPos.x, viewportPos.y, 20.0, 20.0), timer);    
     
 }