iTween - Null Reference

I am using iTween for most part of my game. It was OK until yesterday. Suddenly one of the GameObject Initiate function give me this error:

 NullReferenceException: Object reference not set to an instance of an object
 iTween.RetrieveArgs () (at Assets/Plugins/Pixelplacement/iTween/iTween.cs:6811)
 iTween.Awake () (at Assets/Plugins/Pixelplacement/iTween/iTween.cs:6559)
 UnityEngine.Object:Instantiate(Object, Vector3, Quaternion)

every time I start the game I am getting 320 calls of this errors . But later it accumulate to 720 and now 999+, which I believe it is still accumulating. What is going on and how to resolve this?