title: error The GridView 'GridView1' fired event Sorting which wasn't handled
body: <p>I am trying to Create two groups In  Data Grid like this example <a href="http://www.agrinei.com/gridviewhelper/gridviewhelper_en.htm" rel="noreferrer">http://www.agrinei.com/gridviewhelper/gridviewhelper_en.htm</a>
  but there are an error and I don't know what is the reason or how to solve it 
  <img src="https://i.stack.imgur.com/ovG06.png" alt="enter image description here"></p>