Hi the error the gone after undeploy and redeploy my application to weblogic server. I think the jbpm5.1 jar were cached by weblogic somewhere. It was not an jBPM issue.
The SyncWSHumanTaskHandler is working like a charm ~!
Btw, for those who is interested to use the same core engine transaction for your human task. You need to set the transactionType in your java code.
| | TaskServiceSession tSession = newTaskService().createSession(); |
| | tSession.setTransactionType("local-JTA"); |