PollingDuplex doesn't work in IIS Express

[wakawaka]

I have never use pollingDuplex, but my I ask why you are using it? It seems harder to use than it is worth.

Since it is a chat application, when the server receives a message the server should push to the clients, which you can accomplish with simple duplex calls. Just define a callback on the service contract and make the operational contract that should update the clients one way. Then when you add a service reference to the client, it will automatically create the callback interface that you will have to flesh out.

With this you have a place for the service to "talk" to the client and you can also define events so when the callback gets a message, you raise an event the client is subscribed to.

If you REALLY want to use the polling, do as lighting suggests and get more detail on the error. Add a Trace to the config file and look it over.

<system.diagnostics>
    <sources>
      <source name="System.ServiceModel" switchValue="Error" propagateActivity="true">
        <listeners>
          <add name="ServiceTraceListener" type="System.Diagnostics.XmlWriterTraceListener" initializeData="C:\Temp\MyTrace.log" />
        </listeners>
      </source>
    </sources>
  </system.diagnostics>