WF Integrate ESB issue

I use the workflow which is from Neuron ESB sample and 'SampleWorkflow.esb'.I have set up the pipelines and select the certain assembly.The Workflow can be started by NeuronTestClient.exe which application is installed with Neuron ESB, and the test in the pipeline tab is success. I think there is something wrong in my test application.

Sending Order message
Exception: Neuron.Esb.Channels.ChannelSendException: The pipeline failed while s
ending the message. Unable to create workflow. Make sure the workflow assembly i
s in the GAC or the Neuron folder. ---> Neuron.Pipelines.PipelineException: Unab
le to create workflow. Make sure the workflow assembly is in the GAC or the Neur
on folder. ---> System.ArgumentNullException: Value cannot be null.
Parameter name: workflowType
at System.Workflow.Runtime.WorkflowRuntime.CreateWorkflow(Type workflowType,
Dictionary`2 namedArgumentValues, Guid instanceId)
at System.Workflow.Runtime.WorkflowRuntime.CreateWorkflow(Type workflowType,
Dictionary`2 namedArgumentValues)
at Neuron.Pipelines.WorkflowPipelineStep`1.executeWorkflow(PipelineContext`1
state, Dictionary`2 arguments)
--- End of inner exception stack trace ---
at Neuron.Pipelines.WorkflowPipelineStep`1.executeWorkflow(PipelineContext`1
state, Dictionary`2 arguments)
at Neuron.Pipelines.WorkflowPipelineStep`1.OnExecute(PipelineContext`1 state)

at Neuron.Pipelines.PipelineStep`1.Execute(PipelineContext`1 state)
at Neuron.Pipelines.PipelineInstance`1.Execute(T state)
--- End of inner exception stack trace ---
at Neuron.Esb.Internal.PipelineRuntimeHelper.ApplyPipelines(ESBClientContext
context, ESBMessage& message, Boolean applyOnPublish, Boolean applyOnReceive)
at Neuron.Esb.Internal.PipelineRuntimeHelper.ApplyPublishPipelines(ESBClientC
ontext context, ESBMessage& message)
at Neuron.Esb.Party.SendMessage(ESBMessage message, Boolean duplicateMessage)

at Neuron.Esb.Party.SendMessage(ESBMessage message, SendOptions options, Stri
ng targetId, String action, String schema)
at Neuron.Esb.Party.Send(String topic, Object obj, SendOptions options, Strin
g targetId, DateTime expires, String action, String schema)
at Neuron.Esb.Party.Send(String topic, Object obj, SendOptions options, Strin
g targetId, DateTime expires, String schema)
at Neuron.Esb.Party.Send(String topic, Object obj, SendOptions options, Strin
g targetId)
at Neuron.Esb.Party.Send(String topic, Object obj)
at WFPublisher.Program.Main(String[] args) in D:\Demo\NeuronSamples\Features\
Pipelines\Workflow\WorkflowAlterMessage\WFPublisher\Program.cs:line 35
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