Este erro ocorre porque você colocou os arquivos do hibernate no
classpath do iReport e nao copiou para um diretorio do classPath
ava.lang.IllegalAccessError: tried to access method org.hibernate.engine.CascadeStyle.<init>()V from class org.hibernate.engine.EJB3CascadeStyle$1
at org.hibernate.engine.EJB3CascadeStyle$1.<init>(EJB3CascadeStyle.java:24)
at org.hibernate.engine.EJB3CascadeStyle.<clinit>(EJB3CascadeStyle.java:19)
at org.hibernate.ejb.event.EJB3PersistEventListener.<clinit>(EJB3PersistEventListener.java:19)
at org.hibernate.ejb.EventListenerConfigurator.<init>(EventListenerConfigurator.java:81)
at org.hibernate.ejb.Ejb3Configuration.<init>(Ejb3Configuration.java:136)
at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:124)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:83)
at com.jaspersoft.ireport.designer.connection.EJBQLConnection.getEntityManager(EJBQLConnection.java:129)
at com.jaspersoft.ireport.designer.connection.EJBQLConnection$1.run(EJBQLConnection.java:179)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:226)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:602)
at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:194)
at java.awt.Dialog$1.run(Dialog.java:1072)
at java.awt.Dialog$3.run(Dialog.java:1126)
at java.security.AccessController.doPrivileged(Native Method)
[Solucao]
Apague estes arquivos do classPath e coloque na pasta
a relação de arquivos abaixo
antlr-2.7.6.jar
asm-attrs.jar
asm.jar
cglib-2.1.3.jar
commons-collections-2.1.1.jar
commons-logging-1.1.jar
dom4j-1.6.1.jar
ehcache-1.2.3.jar
ejb3-persistence.jar
hibernate3.jar
hibernate-annotations.jar
hibernate-commons-annotations.jar
hibernate-entitymanager.jar
hibernate-tools.jar
javassist.jar
jaybird-full-2.1.6.jar
jdbc2_0-stdext.jar
jta.jar
jtidy-r8-20060801.jar