NullPointerException au demarage de tomcat

Bonjour,

je suis en JRE5, sur tomcat 6, JPA. j'ai deja reussi à demarrer mon appli, et maintenant j'obtient l'erreur suivante :
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GRAVE: action: null
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in ServletContext resource [/WEB-INF/spring/******-jpa.xml]: Invocation of init method failed; nested exception is java.lang.NullPointerException
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1336)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:471)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
	at java.security.AccessController.doPrivileged(Native Method)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:220)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:423)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:729)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:381)
	at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:255)
	at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:199)
	at org.springframework.web.context.ContextLoaderServlet.init(ContextLoaderServlet.java:81)
	at javax.servlet.GenericServlet.init(GenericServlet.java:212)
	at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1161)
	at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:981)
	at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4045)
	at org.apache.catalina.core.StandardContext.start(StandardContext.java:4351)
	at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
	at org.apache.catalina.core.StandardHost.start(StandardHost.java:719)
	at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
	at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
	at org.apache.catalina.core.StandardService.start(StandardService.java:516)
	at org.apache.catalina.core.StandardServer.start(StandardServer.java:710)
	at org.apache.catalina.startup.Catalina.start(Catalina.java:566)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:585)
	at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:288)
	at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:413)
Caused by: java.lang.NullPointerException
	at org.hibernate.cfg.AnnotationConfiguration.processFkSecondPassInOrder(AnnotationConfiguration.java:440)
	at org.hibernate.cfg.AnnotationConfiguration.secondPassCompile(AnnotationConfiguration.java:304)
	at org.hibernate.cfg.Configuration.buildMappings(Configuration.java:1121)
	at org.hibernate.ejb.Ejb3Configuration.buildMappings(Ejb3Configuration.java:1225)
	at org.hibernate.ejb.EventListenerConfigurator.configure(EventListenerConfigurator.java:159)
	at org.hibernate.ejb.Ejb3Configuration.configure(Ejb3Configuration.java:854)
	at org.hibernate.ejb.Ejb3Configuration.configure(Ejb3Configuration.java:425)
	at org.hibernate.ejb.HibernatePersistence.createContainerEntityManagerFactory(HibernatePersistence.java:131)
	at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:227)
	at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:273)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1367)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1333)
	... 33 more
j'ai testé de nettoyer mon serveur, j'ai verifier mon classpath.

les seuls modifications que j'ai effectué etait dans mon mapping et j'ai supprimé les inclusions des fichiers xml. et l'erreur ne survient que lorsque je place mon tag pour entityManagerFactory.

là je commence a deprimer, auriez vous une idee ? une piste ?
merci