Hello! I have a strange problem, which I don't have in my company related to the usage of mapped superclasses. I have a base entity which encapsulates the id like this: @MappedSuperclass public abstract class SimpleEntity<T extends Serializable> implements Serializable { private static final long serialVersionUID = 1L; private T id; @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "idGenerator") @Column(name = "id", nullable = false, insertable = false, updatable = false) public T getId() { return id; } public void setId(T id) { this.id = id; } } A concrete class example looks like: @Entity @SequenceGenerator(name = "idGenerator", sequenceName = "my_entity_seq", initialValue = 1, allocationSize = 1) public class MyEntity extends SimpleEntity<Integer> { private static final long serialVersionUID = 1L; private String name; public String getName() { return name; } public void setName(T name) { this.name = name; } } But when I try to start the application I get the following error: Caused by: org.hibernate.AnnotationException: Unknown Id.generator: idGenerator at org.hibernate.cfg.BinderHelper.makeIdGenerator(BinderHelper.java:507) at org.hibernate.cfg.AnnotationBinder.processId(AnnotationBinder.java:2126) at org.hibernate.cfg.AnnotationBinder.processElementAnnotations(AnnotationBinder.java:2038) at org.hibernate.cfg.AnnotationBinder.processIdPropertiesIfNotAlready(AnnotationBinder.java:765) at org.hibernate.cfg.AnnotationBinder.bindClass(AnnotationBinder.java:684) at org.hibernate.cfg.Configuration$MetadataSourceQueue.processAnnotatedClassesQueue(Configuration.java:3406) at org.hibernate.cfg.Configuration$MetadataSourceQueue.processMetadata(Configuration.java:3360) at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1334) at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1724) at org.hibernate.ejb.EntityManagerFactoryImpl.<init>(EntityManagerFactoryImpl.java:84) at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:904) ... 9 more This is just a simple example, anyway I have a lot of mapped super classes in my app. Any ideas what the cause of the error might be? The message is not really helpful, also it doesn't point out where the error occurred. Regards, Christian