The EJB 3.0 / JPA compatible Hibernate EntityManager is built on top of Hibernate core and Hibernate Annotations. You have to use compatible versions of each module. This version is known to work on Hibernate Core 3.2.0.CR5, 3.2.0.GA, 3.2.1.GA and Hibernate Annotations 3.2.0.CR3, 3.2.0.GA, 3.2.1.GA. The following libraries have to be in your classpath: hibernate3.jar, hibernate-annotations.jar, hibernate-entitymanager.jar and all needed third party libraries for each package.(incl. ejb-persistence.jar).