title: Contract requires Duplex, but Binding 'BasicHttpBinding' doesn't support it or isn't configured properly to support it
body: <p>I have followed this tutorial for building my chat application. When I try to add reference of my service I get the following error:</p>
  
  <blockquote>
    <p>Contract requires Duplex, but Binding
    'BasicHttpBinding' doesn't support it
    or isn't configured properly to
    support it.</p>
  </blockquote>
  
  <p>My web.config is as follows:</p>
  
  <pre><code>&lt;extensions&gt;
    &lt;bindingExtensions&gt;
      &lt;add name="pollingDuplex" type="System.ServiceModel.Configuration.PollingDuplexHttpBindingCollectionElement,System.ServiceModel.PollingDuplex, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" /&gt;
    &lt;/bindingExtensions&gt;
  &lt;/extensions&gt;
  
  &lt;bindings&gt;      
    &lt;pollingDuplex&gt;
      &lt;binding name="chatPollingDuplex" duplexMode="MultipleMessagesPerPoll"/&gt;
    &lt;/pollingDuplex&gt;
  &lt;/bindings&gt;    
  
  &lt;services&gt;      
    &lt;service name="PrototypeSite.ChatService"&gt;        
      &lt;endpoint address="" binding="pollingDuplex" bindingConfiguration="chatPollingDuplex" contract="PrototypeSite.ChatService" /&gt;
      &lt;endpoint address="mex" binding="wsDualHttpBinding" contract="IMetadataExchange"/&gt;
    &lt;/service&gt;      
  &lt;/services&gt;
  </code></pre>