JTA Transaction and CUrrent Session

We have the following problem. We configured hibernate with jta and when we execute a simple code that performs some hibernate queries we get the following error:

"org.hibernate.LazyInitializationException: could not initialize proxy - the owning Session was closed"

We discovered that if we leave the session opened the error disapears, but on the long run this crashes the server throwing a JDBC connection error.

We tried to use getCurrentSession() instead of opening the session manualy but in this case we get the following error:

"org.hibernate.HibernateException : Unable to locate current UserTransaction"

This its quite strange because the current session should be bound to the current user transaction and its seems to us that our hibernate cfg file its ok.

I´am posting part of my hibernate cfg file and the code that I execute.

hibernate.cfg.xml

<hibernate-configuration>
<session-factory name="java:/hibernate/SessionFactory">

<property name="hibernate.connection.datasource">java:fiap</property>
<property name="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</pro perty>

<!-- Enable Hibernate's automatic session context management -->
<property name="hibernate.current_session_context_class">jta</property>
<property name="hibernate.transaction.factory_class">org.hibernate.transaction. JTATransactionFactory</property>
<property name="hibernate.transaction.manager_lookup_class">org.hibernate.trans action.JBossTransactionManagerLookup</property>
<property name="jta.UserTransaction">java:comp/UserTransaction</property>

<!-- <property name="connection.release_mode">after_statement</property> -->
<!-- <property name="hibernate.transaction.flush_before_completion">true</property>- ->
<property name="hibernate.transaction.auto_close_session">true</property>

.......
......


and my java Code:
.....
try {
tx = HUtil.getTx(); //JNDI lookup
tx.begin();
session = HUtil.getSessionFactory().getCurrentSession(); //JNDI Lookup
//session = HUtil.getSessionFactory().openSession();
Query query = session.createQuery("from Persona where username = ?");
query.setString(0, userName);
persona = (Persona) query.uniqueResult();
query = session.createQuery("from Festival where id = ?");
query.setInteger(0, idFestival);
festival = (Festival) query.uniqueResult();

if (persona != null && festival != null) {
query = session.createQuery("from Inscripcion where inscribeA = :persona " +
"AND inscriptosEn = :festival");
query.setParameter("persona", persona);
query.setParameter("festival", festival);
inscripcion = (Inscripcion) query.uniqueResult();
........
}
.......
return inscripcion;
} catch (Exception e) {
e.printStackTrace();
throw e;
} finally {
tx.commit();
//session.close();
}


thanks