iTween.ValueTo doesn't work?

I am currently using it as such, and the value is not interpolated at all according to what I want.

     float yPos = -10F;
     
     // Use this for initialization
     void Start () {
         iTween.ValueTo(this.gameObject, iTween.Hash("time", 10.0f, "oncomplete", "ContinueUpdate", "oncompleteparams", true, "easetype", iTween.EaseType.spring, "from", yPos, "to", 500F, "onupdate", "UpdatePos"));
     }
     
     void UpdatePos(float newYPos)
     {
         yPos = newYPos;
     }

All that does is just repeatedly calling UpdatePos with no change in the input value, newYPos. I am using the latest version of Unity 4.1.3f3. Am I doing it wrong? Any insights would be appreciated.