Hibernate version:2.1.4

Full stack trace of any exception that occurs:
net.sf.hibernate.JDBCException: could not update: [db.User#890]
at net.sf.hibernate.persister.EntityPersister.update(EntityPersister.java:705)
at net.sf.hibernate.persister.EntityPersister.update(EntityPersister.java:640)
at net.sf.hibernate.impl.ScheduledUpdate.execute(ScheduledUpdate.java:52)
at net.sf.hibernate.impl.SessionImpl.executeAll(SessionImpl.java:2407)
at net.sf.hibernate.impl.SessionImpl.execute(SessionImpl.java:2361)
at net.sf.hibernate.impl.SessionImpl.autoFlushIfRequired(SessionImpl.java:1800)
at net.sf.hibernate.impl.SessionImpl.getQueries(SessionImpl.java:1560)
at net.sf.hibernate.impl.SessionImpl.find(SessionImpl.java:1525)
at net.sf.hibernate.impl.SessionImpl.find(SessionImpl.java:1513)
at net.sf.hibernate.impl.SessionImpl.find(SessionImpl.java:1505)

Name and version of the database you are using: Sybase 12.0

If I do successive find() calls which result in retrieving the same object, I get this exception. What could explain it?