JBoss4.0.0 + Hibernate2.1.5 Transaction problem

[jetrix]

Hi all:
I used a hibernate service with JBoss4.0.0, the configure file:
hibernate-service.xml

<server>
 <mbean code="org.jboss.hibernate.jmx.Hibernate"
 name="jboss.har:service=OracleHibernate">
 <attribute name="DatasourceName">java:OracleDS</attribute>
 <attribute name="Dialect">net.sf.hibernate.dialect.OracleDialect</attribute>
 <attribute name="SessionFactoryName">java:/hibernate/OracleSessionFactory</attribute>
 <attribute name="CacheProviderClass">net.sf.hibernate.cache.TreeCacheProvider</attribute>
 </mbean>
</server>

the Oracle-ds.xml:

<?xml version="1.0" encoding="UTF-8"?>

<!-- ===================================================================== -->
<!-- -->
<!-- JBoss Server Configuration -->
<!-- -->
<!-- ===================================================================== -->

<!-- $Id: oracle-ds.xml,v 1.6 2004/09/15 14:37:40 loubyansky Exp $ -->
<!-- ==================================================================== -->
<!-- Datasource config for Oracle originally from Steven Coy -->
<!-- ==================================================================== -->


<datasources>
 <local-tx-datasource>
 <jndi-name>OracleDS</jndi-name>
 <connection-url>jdbc:oracle:thin:@127.0.0.1:1521:testdb</connection-url>
 <!--

 Here are a couple of the possible OCI configurations.
 For more information, see http://otn.oracle.com/docs/products/oracle9i/doc_library/release2/java.920/a96654/toc.htm

 <connection-url>jdbc:oracle:oci:@youroracle-tns-name</connection-url>
 or
 <connection-url>jdbc:oracle:oci:@(description=(address=(host=youroraclehost)(protocol=tcp)(port=1521))(connect_data=(SERVICE_NAME=yourservicename)))</connection-url>

 Clearly, its better to have TNS set up properly.
 -->
 <driver-class>oracle.jdbc.driver.OracleDriver</driver-class>
 <user-name>jetrix</user-name>
 <password>jetrix</password>

 <!-- Uses the pingDatabase method to check a connection is still valid before handing it out from the pool -->
 <!--valid-connection-checker-class-name>org.jboss.resource.adapter.jdbc.vendor.OracleValidConnectionChecker</valid-connection-checker-class-name-->
 <!-- Checks the Oracle error codes and messages for fatal errors -->
 <exception-sorter-class-name>org.jboss.resource.adapter.jdbc.vendor.OracleExceptionSorter</exception-sorter-class-name>
 <!-- sql to call when connection is created
 <new-connection-sql>some arbitrary sql</new-connection-sql>
 -->

 <!-- sql to call on an existing pooled connection when it is obtained from pool - the OracleValidConnectionChecker is prefered
 <check-valid-connection-sql>some arbitrary sql</check-valid-connection-sql>
 -->

 <!-- corresponding type-mapping in the standardjbosscmp-jdbc.xml (optional) -->
 <metadata>
 <type-mapping>Oracle10g</type-mapping>
 </metadata>
 </local-tx-datasource>

</datasources>

at begin it work well , but in 5 to 6 minutes, the JBoss return a WARNING:

11:10:07,688 WARN [TransactionImpl] Transaction TransactionImpl:XidImpl[FormatId=257, GlobalId=matrix/14, BranchQual=, localId=14] timed out. status=STATUS_ACTIVE

and jsp return :

could not register synchronization with JTA TransactionManager

why? Please help me.