I am getting some intermittent problems with low-level exceptions inside the Hibernate code. The code is multi-threaded which makes things much trickier and I will post updates as information becomes available.

Hibernate version: 3.3.1

Full stack trace of any exception that occurs:
java.util.ConcurrentModificationException
at java.util.LinkedHashMap$LinkedHashIterator.nextEntry(LinkedHashMap.java:365)
at java.util.LinkedHashMap$EntryIterator.next(LinkedHashMap.java:384)
at java.util.LinkedHashMap$EntryIterator.next(LinkedHashMap.java:383)
at org.hibernate.util.IdentityMap.entryArray(IdentityMap.java:228)
at org.hibernate.util.IdentityMap.concurrentEntries(IdentityMap.java:89)
at org.hibernate.event.def.AbstractFlushingEventListener.prepareEntityFlushes(AbstractFlushingEventListener.java:136)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:88)
at org.hibernate.event.def.DefaultAutoFlushEventListener.onAutoFlush(DefaultAutoFlushEventListener.java:58)
at org.hibernate.impl.SessionImpl.autoFlushIfRequired(SessionImpl.java:996)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1141)
at org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
at org.hibernate.impl.AbstractQueryImpl.uniqueResult(AbstractQueryImpl.java:835)
at edu.stsci.synphot.WavelengthRange.getByGlobalID(WavelengthRange.java:30)
at edu.stsci.db.replicationHandlers.SynphotThroughputFileHandler.parseMessage(SynphotThroughputFileHandler.java:97)
at edu.stsci.db.ReplicationSuite$MockReceiver.parseMessage(ReplicationSuite.java:887)
at edu.stsci.db.ReplicationSuite$MockReceiver.handleMessage(ReplicationSuite.java:792)
at edu.stsci.db.StreamHandler.readInputStream(StreamHandler.java:106)
at edu.stsci.db.StreamHandler.doIO(StreamHandler.java:35)
at edu.stsci.db.ReplicationSuite$MockReceiver.run(ReplicationSuite.java:760)

Name and version of the database you are using: Derby 10.4.2

I've just faced the same problem with 3.3.2GA.

I'm querying for the same object from many parallel threads (Message Driven Beans, glassfish v2.1).