sometimes I am getting following exception on submitting task, this exception occurs rarely and it is happening only in production environment not able to reproduce in local.

java.lang.ClassCastException: org.jbpm.graph.def.Node cannot be cast to org.jbpm.graph.node.TaskNode
  at org.jbpm.graph.node.TaskNode$$FastClassByCGLIB$$923668a4.invoke(<generated>)
  at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:149)
  at org.hibernate.proxy.CGLIBLazyInitializer.intercept(CGLIBLazyInitializer.java:161)
  at org.jbpm.graph.node.TaskNode$$EnhancerByCGLIB$$53e0141a.completionTriggersSignal(<generated>)
  at org.jbpm.taskmgmt.exe.TaskInstance.end(TaskInstance.java:432)
  at org.jbpm.taskmgmt.exe.TaskInstance.end(TaskInstance.java:391)
  at com.liferay.jbpm.WorkflowServiceUtil.completeTask(MonorailWorkflowServiceUtil.java:308)
  at com.liferay.jbpm.WorkflowServiceUtil.process(MonorailWorkflowServiceUtil.java:72)
  at com.liferay.jbpm.servlet.JBPMServlet.service(JBPMServlet.java:67)
  at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
  at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
  at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
  at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
  at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
  at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
  at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
  at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
  at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
  at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
  at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
  at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
  at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
  at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
  at java.lang.Thread.run(Thread.java:745)

Fallowing is my code

private String completeTask(long processInstanceId, String taskName, String transition, long userId, long orgId,
  Map<String, Object> processVariables, long taskInstanceId, String driver, String url, String userName, String password) {
  JbpmContext jbpmContext = null;
  String status = "SUCCESS";
  long taskId = 0;
  Connection con = null;
  try {
  con = DBConnection.getDBConnetion(driver, url, userName, password);
  JbpmConfiguration jbpmConfiguration = JbpmConfiguration.getInstance();
  jbpmContext = jbpmConfiguration.createJbpmContext();
  con.setAutoCommit(false);
  jbpmContext.setConnection(con);
  ProcessInstance processInstance = jbpmContext.getProcessInstance(processInstanceId);
  TaskMgmtInstance taskMgmtInstance = processInstance.getTaskMgmtInstance();
  Collection<TaskInstance> taskInstances = taskMgmtInstance.getTaskInstances();
  for (TaskInstance taskInstance : taskInstances) {
  String strTaskName = taskInstance.getTask().getName();
  taskId = taskInstance.getId();
  // log.info("Complete Task - TaskName:" + strTaskName +
  // ", Task to complete: " +
  // taskName);
  if (taskInstanceId > 0 && taskInstanceId == taskId) {
  log.info("Complete Task - Task to complete:" + strTaskName);


  if (null != processVariables && processVariables.size() > 0) {
  try {
  processVariables.remove("");
  processVariables.remove(null);
  } catch (Exception e) {
  e.printStackTrace();
  }
  taskInstance.addVariables(processVariables);
  }
  log.info("Complete Task - transition:" + transition);
  if (null != transition && transition.length() > 0) {
  taskInstance.end(transition);
  } else {
  taskInstance.end();
  }
  jbpmContext.save(taskInstance);
  break;
  }
  }
  con.commit();
  } catch (Exception e) {
  try {
  con.rollback();
  } catch (SQLException e1) {
  e.printStackTrace();
  }
  status = "FAILED";
  e.printStackTrace();
  } finally {


  jbpmContext.close();
  DBConnection.closeConnection(con);
  }
  }