Receiving NotFound CommunicationException in Silverlight 3 WCF client

I'm getting a very unhelpful CommunicationException when attempting to call a WCF service from Silverlight 3. The message of the exception is "The remote server returned an error: NotFound." Each inner exception parrots that same message. Is there a problem with my setup that could be causing this issue?

Here's my setup. The WCF service is hosted in a Windows service running on the .NET 4.0 platform. It has three endpoints:

• The main endpoint uses a pollingDuplexHttpBinding binding and has the address "DashboardService"
• The metadata exchange endpoint uses a mexHttpBinding binding and has the address "mex"
• The policy providing endpoint (this needs to allow cross-domain calls) uses a webHttpBinding binding and has the address "".

Here's the whole system.serviceModel section:

<system.serviceModel>
    <extensions>
      <bindingExtensions>
        <add name="pollingDuplexHttpBinding" type="System.ServiceModel.Configuration.PollingDuplexHttpBindingCollectionElement, System.ServiceModel.PollingDuplex, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      </bindingExtensions>
    </extensions>
    <behaviors>
      <serviceBehaviors>
        <behavior name="">
          <serviceMetadata httpGetEnabled="true" />
          <serviceDebug includeExceptionDetailInFaults="true" />
        </behavior>
      </serviceBehaviors>
      <endpointBehaviors>
        <behavior name="PolicyProviderBehavior">
          <webHttp/>
        </behavior>
      </endpointBehaviors>
    </behaviors>
    <services>
      <service name="RoboTrader.TheFloor.DashboardService">
        <endpoint address="" binding="webHttpBinding"
          behaviorConfiguration="PolicyProviderBehavior"
          contract="RoboTrader.DashboardService.IPolicyProvider"/>
        <endpoint address="DashboardService" binding="pollingDuplexHttpBinding"
          contract="RoboTrader.DashboardService.IDashboardService"/>
        <endpoint address="DashboardService/mex" binding="mexHttpBinding" 
          contract="IMetadataExchange" />
        <host>
          <baseAddresses>
            <add baseAddress="http://localhost:8732/" />
          </baseAddresses>
        </host>
      </service>
    </services>
</system.serviceModel>

In the Silverlight client code, I added a service reference, and that seems to have worked just fine. And the client fetches the cross-domain policy on the service as expected. However, when I call the main DashboardService methods, I get the CommunicationException, and a breakpoint in my server-side method is never reached. Here's the Silverlight ClientConfig file generated by adding the service reference:

<system.serviceModel>
    <bindings>
        <customBinding>
            <binding name="PollingDuplexHttpBinding_IDashboardService">
                <binaryMessageEncoding />
                <httpTransport maxReceivedMessageSize="2147483647"
                  maxBufferSize="2147483647" />
            </binding>
        </customBinding>
    </bindings>
    <client>
        <endpoint address="http://localhost:8732/DashboardService" 
            binding="customBinding"
            bindingConfiguration="PollingDuplexHttpBinding_IDashboardService"
            contract="Service.IDashboardService" 
            name="PollingDuplexHttpBinding_IDashboardService" />
    </client>
</system.serviceModel>

Are there any problems with this setup, or are there any additional things I need to do to get a polling duplex HTTP binding to work? Or do you at least know of how I can get more information about what the issue is?

Edit:

I just tried setting up the client and server bindings through code instead to see if it would help, but I still get the identical exception. Here's the server code:

var dboardService = new DashboardService();
ServiceHost host = new ServiceHost(dboardService);
host.AddServiceEndpoint(
    typeof(IDashboardService),
    new CustomBinding(
        new PollingDuplexBindingElement(),
        new BinaryMessageEncodingBindingElement(),
        new HttpTransportBindingElement()),
    "DashboardService");
host.Open();

And here's the client code:

private IDashboardService _svc = new DashboardServiceClient(
    new PollingDuplexHttpBinding(),
    new EndpointAddress("http://localhost:8732/DashboardService"));

Edit 2:

I tried changing the client code to this, but the same issue occurs:

private IDashboardService _svc = new DashboardServiceClient(
    new CustomBinding(
        new PollingDuplexBindingElement(),
        new BinaryMessageEncodingBindingElement(),
        new HttpTransportBindingElement()),
    new EndpointAddress("http://localhost:8732/DashboardService"));