Problème avec Hibernate 4 et GWT 2.1.0

Salut,
Je travaille avec GWT-2.1.0 et hibernate 3.
AVec cette configuration,je n'ai aucun problème sauf le jours ou j'ai eu besoin de migrer vers hibernate 4,j'ai l'exception suivante qui se pose:

Code:

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[ERROR] org.hibernate.HibernateException: Could not instantiate dialect class [ERROR] at org.hibernate.service.jdbc.dialect.internal.DialectFactoryImpl.constructDialect(DialectFactoryImpl.java:82) [ERROR] at org.hibernate.service.jdbc.dialect.internal.DialectFactoryImpl.buildDialect(DialectFactoryImpl.java:64) [ERROR] at org.hibernate.engine.jdbc.internal.JdbcServicesImpl.configure(JdbcServicesImpl.java:148) [ERROR] at org.hibernate.service.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:75) [ERROR] at org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:159) [ERROR] at org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:131) [ERROR] at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:71) [ERROR] at org.hibernate.cfg.Configuration.buildSettingsInternal(Configuration.java:2270) [ERROR] at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:2266) [ERROR] at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1735) [ERROR] at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1775) ............... [ERROR] Caused by: java.lang.ClassCastException: org.hibernate.dialect.Oracle9iDialect cannot be cast to org.hibernate.dialect.Dialect [ERROR] at org.hibernate.service.jdbc.dialect.internal.DialectFactoryImpl.constructDialect(DialectFactoryImpl.java:73) [ERROR] ... 45 more [INFO] 11:14:22,062 WARN GWTRPCServiceExporter:255 - java.lang.ExceptionInInitializerError [INFO] fail...:null

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