unable to get current rating from a rating control

Hi,

I have a rating control inside a modalpopup.i am unable to get the current raing from the rating control.always it is showing 0.this is my code

 protected void btn_Submit_Click(object sender, EventArgs e)
       {
           string rating = UserRating.CurrentRating.ToString();
       }

<ajaxToolkit:Rating ID="UserRating" runat="server"  MaxRating="5"
     CssClass="rateStar2" StarCssClass="rateItem" WaitingStarCssClass="SaveStar"
     FilledStarCssClass="FillStar" EmptyStarCssClass="EmptyStar"       
     AutoPostBack="false" HorizontalAlign="Left" ></ajaxToolkit:Rating>