How to revisit an old state in jbpm 3.2.8?

[buatapa]

I tried the followings using jbpm 3.2.8. When I end with "no", which should go back to the previous state (submitForm), but I got the following errors occasionally. Did I do something wrong, or what is the right way?

Caused by:

java.util.ConcurrentModificationException

at java.util.HashMap$HashIterator.nextEntry(

HashMap.java:793

)

at java.util.HashMap$KeyIterator.next(

HashMap.java:828

)

at org.hibernate.collection.AbstractPersistentCollection$IteratorProxy.next(

AbstractPersistentCollection.java:555

)

java code (I am in open approveForm state)

Collection taskList = processInstance.getTaskMgmtInstance().getTaskInstances();

Iterator<?> iter = taskList.iterator();

while (iter.hasNext()) {

       TaskInstance taskInstance = (TaskInstance) iter.next();

        if (taskInstance.isOpen()) {

               taskInstance.end(approve ?

"yes" :"no");

        }

}

......

process definition code

<start-state name="start">
  <transition to="submitForm"></transition>
</start-state>

<task-node name="submitForm">
  <task name="submitForm">
   <assignment actor-id="submitter"></assignment>
  </task>
  <transition to="approveForm"></transition>
</task-node>

<task-node name="approveForm">
  <task name="approveForm">
   <assignment actor-id="approver"></assignment>
  </task>
  <transition to="end" name="yes"></transition>
  <transition to="submitForm" name="no"></transition>
</task-node>

<end-state name="end">
</end-state>