Thanks for your  help.  I also tried this and it worked as well-

 protected void Page_Load(System.Object sender, System.EventArgs e)
{
            Microsoft.Web.UI.ScriptManager sm =               (Microsoft.Web.UI.ScriptManager)Microsoft.Web.UI.ScriptManager.GetCurrent(this.Page);

            sm.RegisterAsyncPostBackControl(RadioButtonList1);
          
}

The second problem I have is I cant get my AutoCompleteExtender to change it's ServiceMethod when the SelectedIndexChanged event occurs.  It works when the page first loads, but when you click on a radio button I need to change the ServiceMethod of the AutoCompleteExtender and it quits working altogether so that is not good :(