Silverlight: WCF obtiene un error en el servidor pero localhost funciona bien

Tengo la aplicación Silverlight y recibo este error:

[Async_ExceptionOccurred]
Arguments: 
Debugging resource strings are unavailable. Often the key and arguments provide sufficient information to diagnose the problem. See http://go.microsoft.com/fwlink/?linkid=106663&Version=5.0.61118.00&File=System.dll&Key=Async_ExceptionOccurred INNER >System.ServiceModel.CommunicationException: [CrossDomainError]
Arguments: http://localhost/pthaba/SimpleWCF.svc
Debugging resource strings are unavailable. Often the key and arguments provide sufficient information to diagnose the problem. See http://go.microsoft.com/fwlink/?linkid=106663&Version=5.0.61118.00&File=System.ServiceModel.dll&Key=CrossDomainError ---> System.Security.SecurityException ---> System.Security.SecurityException: [Arg_SecurityException]
Arguments: 
Debugging resource strings are unavailable. Often the key and arguments provide sufficient information to diagnose the problem. See http://go.microsoft.com/fwlink/?linkid=106663&Version=5.0.61118.00&File=mscorlib.dll&Key=Arg_SecurityException

Tengo un servicio WCF y funciona bien en el navegador. Tengo clientacesspolicy.xml como a continuación en el sitio raíz (donde se encuentra el servicio WCF)

<?xml version="1.0" encoding="utf-8" ?>
<access-policy>
  <cross-domain-access>
    <policy>
      <allow-from >
        <domain uri="*"/>
      </allow-from>
      <grant-to>
        <resource path="/" include-subpaths="true"/>
      </grant-to>
    </policy>

  </cross-domain-access>
</access-policy>

¿Qué estoy haciendo mal? ¿Alguien puede ayudarme?

EDIT:

En mi localhost funciona bien, pero en el servidor no. Fiddler parece estar bien, no hay error en eso.

¿Me estoy perdiendo alguna configuración de IIS?

Más detalles del error arriba:

 at System.Net.Browser.BrowserHttpWebRequest.InternalEndGetResponse(IAsyncResult asyncResult)
   at System.Net.Browser.BrowserHttpWebRequest.<>c__DisplayClassa.<EndGetResponse>b__9(Object sendState)
   at System.Net.Browser.AsyncHelper.<>c__DisplayClass4.<BeginOnUI>b__1(Object sendState)
   --- End of inner exception stack trace ---
   at System.Net.Browser.AsyncHelper.BeginOnUI(SendOrPostCallback beginMethod, Object state)
   at System.Net.Browser.BrowserHttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
   at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelAsyncRequest.CompleteGetResponse(IAsyncResult result)
   --- End of inner exception stack trace ---
   at System.ServiceModel.AsyncResult.End[TAsyncResult](IAsyncResult result)
   at System.ServiceModel.Channels.ServiceChannel.SendAsyncResult.End(SendAsyncResult result)
   at System.ServiceModel.Channels.ServiceChannel.EndCall(String action, Object[] outs, IAsyncResult result)
   at System.ServiceModel.ClientBase`1.ChannelBase`1.EndInvoke(String methodName, Object[] args, IAsyncResult result)
   at Pthaba.SimpleSVC.SimpleWCFClient.SimpleWCFClientChannel.EndGetGameLevelPlataforms(IAsyncResult result)
   at Pthaba.SimpleSVC.SimpleWCFClient.Pthaba.SimpleSVC.ISimpleWCF.EndGetGameLevelPlataforms(IAsyncResult result)
   at Pthaba.SimpleSVC.SimpleWCFClient.OnEndGetGameLevelPlataforms(IAsyncResult result)
   at System.ServiceModel.ClientBase`1.OnAsyncCallCompleted(IAsyncResult result)
ult)