JPA and composite primary key

Hi.
Here's the scenario:
An abstract class that defines an Id "generated":
public abstract Class1{
[...]
@Column(name = "ID")
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "IdSequenceGen")
@Id
public Long getId()
{
return this.id;
}
[...]
}

An entity Class, extending Class1, that has a composite PK: The 'Class1' ID and a second field:

@Entity
@IdClass(Class2.class)
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@SequenceGenerator(name = "IdSequenceGen", sequenceName = "SQ_CLASS2")
@Table(name = "CIM_PERSON_DEMOGRAPHIC")
public class Class2 extends Class1{
private Integer prog = 0;

@Column(name = "PROG")
@Id
public Integer getProg()
{
return prog;
}
[...]
}

But in this case I've this error at runtime:
javax.persistence.PersistenceException: [PersistenceUnit: datamodel] Unable to configure EntityManagerFactory
at org.hibernate.ejb.Ejb3Configuration.configure(Ejb3Configuration.java:375)
at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:56)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:48)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:32)
at com.noemalife.platform.dm.test.AbstractTest.buildEntityManager(AbstractTest.java:111)
Caused by: org.hibernate.AnnotationException: Unknown Id.generator: IdSequenceGen

How can i solve this problem?

Thank you so much
.