Silverlight Web Resource AsyncCallback Exception on Retrieve Multiple

I have a method which performs and simple RetrieveMultiple, and the call back method loops through the attributes and performs some formatting.

The code works as a plugin, so I am quite sure that the logic is right.

When the request itself is executed, I get the following error

SCRIPT5022: Unhandled Error in Silverlight Application An AsyncCallback threw an exception.   at System.ServiceModel.AsyncResult.Complete(Boolean completedSynchronously)
   at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelAsyncRequest.OnGetResponse(IAsyncResult result)
   at System.Net.Browser.BrowserHttpWebRequest.<>c__DisplayClass19.<InvokeGetResponseCallback>b__17(Object state2)
   at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback() 

The code that performs the request is as below

  QueryExpression query = new QueryExpression()
            {
                EntityName = "contact",
                ColumnSet = new ColumnSet()
                {
                    //AllColumns = true
                },
            };
            OrganizationRequest request = new OrganizationRequest() { RequestName = "RetrieveMultiple" };
            request.Parameters = new ParameterCollection();
            request.Parameters.Add(new KeyValuePair<string, object>("Query", query));
            //request["Query"] = query;
            IOrganizationService service = SilverlightUtility.GetSoapService(org_url);

            //  service.BeginExecute(request, new AsyncCallback(performSearch), service);

            service.BeginRetrieveMultiple(query, (result) =>
            {
                throw new Exception("before get response");
                var response = ((IOrganizationService)result.AsyncState).EndRetrieveMultiple(result);
                Dispatcher.BeginInvoke(new Action(
            () =>
            {
                performSearch2(response.Entities);

            }));
            }, service);

Am I missing something glaringly obvious?

Thanks!