oracle10g bug

when I test sample with oracle , if I don't open a connection here , 
fail trace will be this : 
javax.persistence.PersistenceException: [PersistenceUnit: org.jbpm.persistence.jpa] Unable to build EntityManagerFactory
	at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:930)
	at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:904)
	at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:72)
	at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:63)
	at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:47)