For human task serveice you should start the human task server before you register the handler.
Folowing is the code for starting the Mina Task server.
EntityManagerFactory emfTask = Persistence.createEntityManagerFactory("org.jbpm.task");
TaskService taskService = new TaskService(emfTask,SystemEventListenerFactory.getSystemEventListener());
TaskServiceSession taskSession = taskService.createSession();
MinaTaskServer minaTaskServer = newMinaTaskServer(taskService,9123);
Thread thread = new Thread(minaTaskServer ));
thread.start();