hibernate报错。。。

08:33:30,031 ERROR DTDEntityResolver:72 - Don't use old DTDs, read the Hibernate 3.x Migration Guide!
 Hibernate: select seq.nextval from dual
Exception in thread "main" org.hibernate.HibernateException: identifier of an instance of com.donna.model.Role was altered from 152 to 152
at org.hibernate.event.def.DefaultFlushEntityEventListener.checkId(DefaultFlushEntityEventListener.java:81)
at org.hibernate.event.def.DefaultFlushEntityEventListener.getValues(DefaultFlushEntityEventListener.java:187)
at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:143)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:219)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:99)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:49)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1028)
at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:366)
at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:137)
at Test.test(Test.java:36)
at Test.main(Test.java:21)
===================================
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.donna.model.Role" table="ROLES">
        <id name="id" type="java.lang.Integer">
            <column name="roles_id" />
        <generator class="sequence">
         <param name="sequence">seq</param>
        </generator>
        </id>
        <property name="name" type="java.lang.String">
            <column name="ROLE_NAME" length="50" not-null="true" unique="true" />
        </property>
    </class>
</hibernate-mapping>
========================================
请问这是什么原因啊。