Java Server Faces and Java Persistence API - Newbie problem

Hello,

I've got this simple Book-class, whose objects should be stored in a
database:
im****t java.io.Serializable;
im****t javax.persistence.Entity;
im****t javax.persistence.GeneratedValue;
im****t javax.persistence.Id;
im****t javax.persistence.NamedQuery;

@[EMAIL PROTECTED]
(name = "findAllBooks", query = "SELECT OBJECT(bk) from
Book bk")
public class Book implements Serializable {
	private Long id;
	private String author;
	private String title;
	private boolean available;

	// [...]

	@[EMAIL PROTECTED]
 Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	// [...]
}

I've written the following session bean to handle serialization of the
Book-objects:
im****t javax.annotation.Resource;
im****t javax.persistence.EntityManager;
im****t javax.persistence.PersistenceContext;
im****t javax.transaction.UserTransaction;

public class BookBean {
	@[EMAIL PROTECTED]
(unitName="books")
	private EntityManager em;
	@[EMAIL PROTECTED]
 UserTransaction utx;
	private Book currentBook = new Book();

	// [...]

	public String submitBook() {
		try {
			utx.begin();
			em.persist(currentBook);
			utx.commit();
		} catch (Exception e) {
			try {
				utx.rollback();
			} catch (Exception e1) {
				e1.printStackTrace();
			}
			e.printStackTrace();
		}
		currentBook = null;
		return "submitBook";
	}
	// [...]
}

The submitBook()-method of the BookBean is called by a .jsp-File from
which the user can create a new Book-object, which is stored in the
currentBook-object. However, when the program reaches the utx.commit()-
statement the following Exception is thrown:
java.lang.IllegalStateException: During synchronization a new object
was found through a relation****p that was not marked cascade PERSIST.

        at
oracle.toplink.essentials.internal.ejb.cmp3.base.RepeatableWriteUnitOfWork
$1.iterate(RepeatableWriteUnitOfWork.java:115)

[...]

Does anyone know why I get this strange exception although I haven't
used any relation****ps at all in my JSF-program?

Thanks for any help.