function ValidateDropDownList(source, arguments) 
{ 
  var ddl = document.getElementById(source.controltovalidate); 

  if (ddl != null) 
  { 
    var selectedValue = new Number(ddl[ddl.selectedIndex].value); 
    arguments.IsValid = (selectedValue > 0); 
  } 
  else 
  {
    arguments.IsValid = false; 
  }
}