Dynamically Loading a UserControl with LoadControl Method (Type, object[])

[WebMethod]
public static string LoadAlternates(string productId, string pnlId)
{
 object[] parameters = new object[] { pnlId, productId };
 return ControlAsString(typeof(PopupControl), parameters);
}

private static string ControlAsString(Type controlType, object[] parameters)
{
 Page page = new Page();
 UserControl controlToLoad;
 /*
  *calling load control with the type results in the
  *stringwriter returning an empty string
  */
 controlToLoad = page.LoadControl(controlType, parameters) as UserControl;
 /*
  *However, calling LoadControl with the following overload
  *gives the correct result, ie the string rep. of the control.
  */
  controlToLoad = page.LoadControl(@"~/RepeaterSamples/PopupControl.ascx") as UserControl;

 //some more code, then this...
 page.Controls.Add(controlToLoad);

 StringWriter sw = new StringWriter();
 HttpContext.Current.Server.Execute(page, sw, false);
 return sw.ToString();
}