Problem with iTween.ValueTo

hello , i want to interpolate float value but the itween still warn that it works only for float ,color, vectors,rect , even i already used float value but it still not work.

// Use this for initialization
void Start () {
iTween.ValueTo(gameObject,iTween.Hash(
"from",0.0f,
"to",1000.0f,
"onupdate","UpdateValue",
"time",1
));
}

// Update is called once per frame
void UpdateValue(float val) {
Debug.Log (val);
}