Enviroment:JBossAS 4.0.3SP1 + JBoss Portal 2.2.1 + MySQL5.0

when create a new user, error occurs:
15:37:52,312 ERROR [AssertionFailure] an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session)
org.hibernate.AssertionFailure: null id in org.jboss.portal.core.impl.user.UserImpl entry (don't flush the Session after an exception occurs)
at org.hibernate.event.def.DefaultFlushEntityEventListener.checkId(DefaultFlushEntityEventListener.java:48)
at org.hibernate.event.def.DefaultFlushEntityEventListener.getValues(DefaultFlushEntityEventListener.java:140)
at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:97)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:195)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEverything
ToExecutions(AbstractFlushingEventListener.java:76)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:26)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:905)
at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:345)
at org.hibernate.transaction.CacheSynchronization.beforeCompletion(CacheSynchronization.java:59)
at org.jboss.tm.TransactionImpl.doBeforeCompletion(TransactionImpl.java:1473)
at org.jboss.tm.TransactionImpl.beforePrepare(TransactionImpl.java:1092)

at org.jboss.tm.TransactionImpl.commit(TransactionImpl.java:306)
at org.jboss.tm.TxManager.commit(TxManager.java:224)
at org.jboss.portal.common.transaction.Transactions.end(Transactions.java:414)
at org.jboss.portal.common.transaction.Transactions$5.noTxAfter(Transactions.java:605)
at org.jboss.portal.common.transaction.Transactions.applyAfter(Transactions.java:122)
at org.jboss.portal.core.aspects.server.TransactionInterceptor.invoke(TransactionInterceptor.java:85)
at org.jboss.portal.server.ServerInterceptor.invoke(ServerInterceptor.java:38)
at org.jboss.portal.server.invocation.Invocation.invokeNext(Invocation.java:130)