Can someone offer some plausible explanation as to why this would work:

 public String ejbCreate(AttendanceBaseDTO dto, Person person, Package regPackage)
 throws ArgumentException, CreateException, DuplicateException {

 try {
 ejbSelectByEventAndPersonEmailAddress(person.getEvent().getId(), person.getEmailAddress());
 //_ctx.setRollbackOnly();
 throw new DuplicateException("AttendanceBean(ejbCreate): an attendance object aleady exists for event "+
 "name \""+person.getEvent().getName()+"\" and person with email address of "+person.getEmailAddress());
 } catch (FinderException ex) {
 // not finding this person is what we are expecting. Finding person is an error as above.
 }

However if I uncomment the setRollback only the code fails with the following exception ...

15:11:42,586 ERROR [BeanLock] Saw rolled back tx=TransactionImpl:XidImpl[FormatId=257, GlobalId=BJSLAP/1451, BranchQual=, localId=1451]
15:11:42,586 ERROR [LogInterceptor] TransactionRolledbackLocalException in method: public abstract com.e2m.beans.entity.Event com.e2m.beans.entity.Person.getEvent(), causedBy:
java.lang.RuntimeException: Transaction marked for rollback, possibly a timeout
 at org.jboss.ejb.plugins.lock.QueuedPessimisticEJBLock.doSchedule(QueuedPessimisticEJBLock.java:228)
 at org.jboss.ejb.plugins.lock.QueuedPessimisticEJBLock.schedule(QueuedPessimisticEJBLock.java:183)
 at org.jboss.ejb.plugins.EntityLockInterceptor.invoke(EntityLockInterceptor.java:85)
 at org.jboss.ejb.plugins.EntityCreationInterceptor.invoke(EntityCreationInterceptor.java:53)
 at org.jboss.ejb.plugins.CallValidationInterceptor.invoke(CallValidationInterceptor.java:48)
 at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:105)
 at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:316)
 at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:149)
 at org.jboss.ejb.plugins.SecurityInterceptor.invoke(SecurityInterceptor.java:128)
 at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:191)
 at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:122)
 at org.jboss.ejb.EntityContainer.internalInvoke(EntityContainer.java:514)
 at org.jboss.ejb.Container.invoke(Container.java:854)
 at org.jboss.ejb.plugins.local.BaseLocalProxyFactory.invoke(BaseLocalProxyFactory.java:413)
 at org.jboss.ejb.plugins.local.EntityProxy.invoke(EntityProxy.java:44)
 at $Proxy757.getEvent(Unknown Source)
 at com.e2m.beans.entity.AttendanceBean.ejbCreate(AttendanceBean.java:534)

I have MySQL configured for InnoDB tables. Is there anything special that needs to be done such that JBoss can roll back the transaction in MySQL??

Many thanks,
Joe