title: telerik radwindow : Value does not fall within the expected range
body: <p>I have two user controls that contain the telerik radwindow. </p>
  
  <p>When I try to open second window on first window button click, I get the below exception: </p>
  
  <blockquote>
    <p>Value does not fall within the expected range</p>
  </blockquote>