I have posted the similar exception before. How to avoid this exception? Why would hibernate read other records when I am trying to read a specific USER record. Hibernate tries to read all the records and bombs with the exception below.

Hibernate version:
Hibernate 2
Mapping documents:
<id name="id" type="long" unsaved-value="null">
<column name="user_id" not-null="true"/>
<generator class="native"/>
</id>

<property name="guid" type="string"/>
<property name="role_id" type="int" />
<property name="first_name" type="string" />
<property name="last_name" type="string"/>
<property name="login_name" type="string"/>
<property name="login_password" type="string"/>
<property name="alias" type="string"/>
<property name="addressBookId" column="address_book_id" type="long"/>
<one-to-one name="addressBook" class="com.tek.web.datasource.hibernate.AddressBook" property-ref="owner" cascade="all"/>

Code between sessionFactory.openSession() and session.close():

public WsServer getServerGraphForUser(final Long userId) throws StorageException {
QueryTask queryTask = new QueryTask(session) {
Object executeTask() throws StorageException, HibernateException {
Query query = session.createQuery("from WsServer server" +
" join fetch server.addressBooks book" +
" where book.ownerId = :userId");
query.setLong("userId", userId.longValue());

return query.uniqueResult();
}
};

return (WsServer) queryTask.execute();
}

Full stack trace of any exception that occurs:
net.sf.hibernate.WrongClassException: Object with id: 6 was not of the specified subclass: com.tek.web.datasource.hibernate.AddressBook (loaded object was of wrong class)
at net.sf.hibernate.loader.Loader.instanceAlreadyLoaded(Loader.java:456)
at net.sf.hibernate.loader.Loader.getRow(Loader.java:423)
at net.sf.hibernate.loader.Loader.doQuery(Loader.java:209)
at net.sf.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:133)
at net.sf.hibernate.loader.Loader.loadCollection(Loader.java:915)
at net.sf.hibernate.loader.Loader.loadCollection(Loader.java:890)
at net.sf.hibernate.loader.OneToManyLoader.initialize(OneToManyLoader.java:93)
at net.sf.hibernate.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:284)
at net.sf.hibernate.impl.SessionImpl.initializeCollection(SessionImpl.java:3264)
at net.sf.hibernate.collection.PersistentCollection.forceInitialization(PersistentCollection.java:336)
at net.sf.hibernate.impl.SessionImpl.initializeNonLazyCollections(SessionImpl.java:3119)
at net.sf.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:138)
at net.sf.hibernate.loader.Loader.loadEntity(Loader.java:836)
at net.sf.hibernate.loader.Loader.loadEntity(Loader.java:856)
at net.sf.hibernate.loader.EntityLoader.load(EntityLoader.java:59)
at net.sf.hibernate.loader.EntityLoader.load(EntityLoader.java:51)
at net.sf.hibernate.persister.EntityPersister.load(EntityPersister.java:419)
at net.sf.hibernate.impl.SessionImpl.doLoad(SessionImpl.java:2113)
at net.sf.hibernate.impl.SessionImpl.doLoadByClass(SessionImpl.java:1987)
at net.sf.hibernate.impl.SessionImpl.internalLoad(SessionImpl.java:1949)
at net.sf.hibernate.type.ManyToOneType.resolveIdentifier(ManyToOneType.java:69)
at net.sf.hibernate.type.EntityType.resolveIdentifier(EntityType.java:204)
at net.sf.hibernate.type.EntityType.nullSafeGet(EntityType.java:126)
at net.sf.hibernate.impl.ScrollableResultsImpl.prepareCurrentRow(ScrollableResultsImpl.java:415)
at net.sf.hibernate.impl.ScrollableResultsImpl.first(ScrollableResultsImpl.java:62)
at com.tek.admin.webapp.AddUserAndGroupsForm.getUsersList(AddUserAndGroupsForm.java:225)
at com.tek.admin.webapp.AddUserAndGroupsForm.reset(AddUserAndGroupsForm.java:208)
at org.apache.struts.action.RequestProcessor.processPopulate(RequestProcessor.java:816)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:254)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:768)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:861)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:118)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)
at java.lang.Thread.run(Unknown Source)

Name and version of the database you are using:
MySQL 4.1
The generated SQL (show_sql=true):

Debug level Hibernate log excerpt: