Workflow hanging at set state robot

For particular workflow processes, it is hanging at the Set State Robot, and throwing the following error. I could not find any root cause for this issue.

A nested transaction cannot be started when a rollback is in progress.  The following is the rollback stacktrace.
   ROLLBACK: java.lang.Thread.getStackTraceImpl(Native Method)
   ROLLBACK: java.lang.Thread.getStackTrace(Thread.java:1042)
   ROLLBACK: wt.pom.TransactionManager.rollbackTransaction(TransactionManager.java:624)
   ROLLBACK: wt.pom.BasicTransactionMonitor.rollbackTransaction(BasicTransactionMonitor.java:77)
   ROLLBACK: wt.pom.PersistentObjectManager.rollbackTransaction(PersistentObjectManager.java:447)
   ROLLBACK: wt.pom.Transaction.rollback(Transaction.java:566)
   ROLLBACK: wt.workflow.engine.StandardWfEngineService.synchRobotToEvent(StandardWfEngineService.java:8959)
   ROLLBACK: wt.workflow.engine.StandardWfEngineService$SynchEventListener.notifyVetoableEvent(StandardWfEngineService.java:429)
   ROLLBACK: wt.events.StandardKeyedEventBranch.intDispatchEvent(StandardKeyedEventBranch.java:320)
   ROLLBACK: wt.events.StandardKeyedEventBranch.dispatchVetoableEvent(StandardKeyedEventBranch.java:229)
   ROLLBACK: wt.events.StandardKeyedEventDispatcher.intDispatchEvent(StandardKeyedEventDispatcher.java:286)
   ROLLBACK: wt.events.StandardKeyedEventDispatcher.dispatchVetoableEvent(StandardKeyedEventDispatcher.java:215)
   ROLLBACK: wt.services.StandardManagerService.intDispatchVetoableEvent(StandardManagerService.java:406)
   ROLLBACK: wt.services.StandardManagerService.dispatchVetoableEvent(StandardManagerService.java:302)
   ROLLBACK: wt.lifecycle.StandardLifeCycleService.dispatchVetoableEvent(StandardLifeCycleService.java:571)
   ROLLBACK: wt.lifecycle.StandardLifeCycleService.doSetState(StandardLifeCycleService.java:9981)
   ROLLBACK: wt.lifecycle.StandardLifeCycleService.doSetState(StandardLifeCycleService.java:7449)
   ROLLBACK: wt.lifecycle.StandardLifeCycleService.setState(StandardLifeCycleService.java:7256)
   ROLLBACK: wt.lifecycle.StandardLifeCycleService.setState(StandardLifeCycleService.java:7587)

If somebody throws some light on this issue, will be very much appreciated.

Thanks

Suresh