Hi jochen, I am getting same exception . i have followed exactly what u have suggested. i am giving my persistence.xml <persistence-unit name="bids"> <jta-data-source>java:/ConnectVendorsMySQL</jta-data-source> </persistence-unit> And SkillLevel class SkillLevelKey primaryKey; @EmbeddedId @AttributeOverrides({ @AttributeOverride(name = "skill_Id", column = @Column(name = "skill_Id")), @AttributeOverride(name = "vendor_Id", column = @Column(name = "vendor_Id")) }) getters and setters for primaryKey. lease tell me where i am doing mistake Thanks&Regards K.Ramu View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4220862#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...