Keep getting BCE0017 error

i keep getting the error Assets/Twin_Cannon.js(30,63): BCE0017: The best overload for the method 'UnityEngine.Quaternion.Lerp(UnityEngine.Quaternion, UnityEngine.Quaternion, float)' is not compatible with the argument list '(UnityEngine.Quaternion, System.Type, float)'. and i dont know why or how to fix, please help

 #pragma strict
 
 var myprojectile : GameObject;
 var reloadTime : float = 1f;
 var turnSpeed : float = 5f;
 var firePauseTime : float = .25f;
 var muzzleEffect : GameObject;
 var errorAmount : float = .001;
 var myTarget : Transform;
 var muzzlePosition : Transform[];
 var turrentBall : Transform;
 
 private var nextFireTime : float;
 private var nextMoveTime :float;
 private var desiredRotation = Quaternion;
 private var aimError : float;
 
 function Start () 
 {
 
 }
 
 function Update () 
 {    
     if(myTarget)
     {
         if(Time.time >= nextMoveTime)
         {
             CalculateAimPosition(myTarget.position);
             turrentBall.rotation = Quaternion.Lerp(turrentBall.rotation,desiredRotation,Time.deltaTime*turnSpeed);
         }