Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect

[newnhibernateUser]

NHibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect
   at NHibernate.Persister.Entity.AbstractEntityPersister.Update(Object id, Object[] fields, Object[] oldFields, Object rowId, Boolean[] includeProperty, Int32 j, Object oldVersion, Object obj, SqlCommandInfo sql, ISessionImplementor session)
   at NHibernate.Persister.Entity.AbstractEntityPersister.UpdateOrInsert(Object id, Object[] fields, Object[] oldFields, Object rowId, Boolean[] includeProperty, Int32 j, Object oldVersion, Object obj, SqlCommandInfo sql, ISessionImplementor session)
   at NHibernate.Persister.Entity.AbstractEntityPersister.Update(Object id, Object[] fields, Int32[] dirtyFields, Boolean hasDirtyCollection, Object[] oldFields, Object oldVersion, Object obj, Object rowId, ISessionImplementor session)
   at NHibernate.Action.EntityUpdateAction.Execute()
   at NHibernate.Engine.ActionQueue.Execute(IExecutable executable)
   at NHibernate.Engine.ActionQueue.ExecuteActions(IList list)
   at NHibernate.Engine.ActionQueue.ExecuteActions()
   at NHibernate.Event.Default.AbstractFlushingEventListener.PerformExecutions(IEventSource session)
   at NHibernate.Event.Default.DefaultFlushEventListener.OnFlush(FlushEvent event)
   at NHibernate.Impl.SessionImpl.Flush()
   at NHibernate.Transaction.AdoTransaction.Commit()