title: missing a using directive or an assembly reference OperationContext
body: <p>In My c# windows form it has a error </p>
  
  <blockquote>
    <p>The type or namespace name 'OperationContext' could not be found (are
    you missing a using directive or an assembly reference?)</p>
  </blockquote>
  
  <p>can any one explain me the reason??</p>