错误信息：

发生了未经处理的异常，已终止进程。

Application ID: /LM/W3SVC/35/ROOT

Process ID: 3912

Exception: System.Runtime.CallbackException

Message: 异步回调引发了异常。

StackTrace:    在 System.Runtime.AsyncResult.Complete(Boolean completedSynchronously)
   在 System.ServiceModel.Activation.HostedHttpRequestAsyncResult.CompleteAsynchronously(Exception ex)
   在 System.ServiceModel.Activation.HostedHttpContext.HostedRequestHttpOutput.HostedResponseOutputStream.Close()
   在 System.ServiceModel.Channels.HttpOutput.Close()
   在 System.ServiceModel.Channels.HttpRequestContext.OnReply(Message message, TimeSpan timeout)
   在 System.ServiceModel.Channels.RequestContextBase.Reply(Message message, TimeSpan timeout)
   在 System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.Reply(MessageRpc& rpc)
   在 System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage9(MessageRpc& rpc)
   在 System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage8(MessageRpc& rpc)
   在 System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc)
   在 System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage31(MessageRpc& rpc)
   在 System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)
   在 System.ServiceModel.Dispatcher.ChannelHandler.DispatchAndReleasePump(RequestContext request, Boolean cleanThread, OperationContext currentOperationContext)
   在 System.ServiceModel.Dispatcher.ChannelHandler.HandleRequest(RequestContext request, OperationContext currentOperationContext)
   在 System.ServiceModel.Dispatcher.ChannelHandler.AsyncMessagePump(IAsyncResult result)
   在 System.Runtime.Fx.AsyncThunk.UnhandledExceptionFrame(IAsyncResult result)
   在 System.Runtime.AsyncResult.Complete(Boolean completedSynchronously)
   在 System.Runtime.InputQueue`1.AsyncQueueReader.Set(Item item)
   在 System.Runtime.InputQueue`1.EnqueueAndDispatch(Item item, Boolean canDispatchOnThisThread)
   在 System.Runtime.InputQueue`1.EnqueueAndDispatch(T item, Action dequeuedCallback, Boolean canDispatchOnThisThread)
   在 System.ServiceModel.Channels.SingletonChannelAcceptor`3.Enqueue(QueueItemType item, Action dequeuedCallback, Boolean canDispatchOnThisThread)
   在 System.ServiceModel.Channels.HttpPipeline.EnqueueMessageAsyncResult.CompleteParseAndEnqueue(IAsyncResult result)
   在 System.ServiceModel.Channels.HttpPipeline.EnqueueMessageAsyncResult.HandleParseIncomingMessage(IAsyncResult result)
   在 System.Runtime.AsyncResult.SyncContinue(IAsyncResult result)
   在 System.ServiceModel.Channels.HttpPipeline.EmptyHttpPipeline.BeginProcessInboundRequest(ReplyChannelAcceptor replyChannelAcceptor, Action dequeuedCallback, AsyncCallback callback, Object state)
   在 System.ServiceModel.Channels.HttpChannelListener`1.HttpContextReceivedAsyncResult`1.ProcessHttpContextAsync()
   在 System.ServiceModel.Channels.HttpChannelListener`1.BeginHttpContextReceived(HttpRequestContext context, Action acceptorCallback, AsyncCallback callback, Object state)
   在 System.ServiceModel.Activation.HostedHttpTransportManager.HttpContextReceived(HostedHttpRequestAsyncResult result)
   在 System.ServiceModel.Activation.HostedHttpRequestAsyncResult.HandleRequest()
   在 System.ServiceModel.Activation.HostedHttpRequestAsyncResult.BeginRequest()
   在 System.ServiceModel.Activation.HostedHttpRequestAsyncResult.OnBeginRequest(Object state)
   在 System.ServiceModel.AspNetPartialTrustHelpers.PartialTrustInvoke(ContextCallback callback, Object state)
   在 System.ServiceModel.Activation.HostedHttpRequestAsyncResult.OnBeginRequestWithFlow(Object state)
   在 System.Runtime.IOThreadScheduler.ScheduledOverlapped.IOCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped)
   在 System.Runtime.Fx.IOCompletionThunk.UnhandledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped)
   在 System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP)

InnerException: System.NullReferenceException

Message: 未将对象引用设置到对象的实例。

StackTrace:    在 System.Web.HttpApplication.PipelineStepManager.ResumeSteps(Exception error)
   在 System.Web.HttpApplication.CallHandlerExecutionStep.OnAsyncHandlerCompletion(IAsyncResult ar)
   在 System.Runtime.AsyncResult.Complete(Boolean completedSynchronously)

求大神