EclipseLink JPA 2 Type not valid for serialized mapping

I get the following error when my application starts first ...

Raised: Exception [EclipseLink-7155] (Eclipse Persistence Services - 2.0.1.v20100213-r6600): org.eclipse.persistence.exceptions.ValidationException Exception Description: Type [class Lap] for attribute [lapId] in entity class [class Novartis .OTM.Data.Db.Entities.DtsTmpClass] is not a valid type for serialized mapping. The attribute type must implement the Serializable interface.

Here are the relevant objects.

@SequenceGenerator(name="SEQ_DTS_TMP_CLASS", sequenceName="SEQ_DTS_TMP_CLASS", allocationSize=1)
@Entity
@Table(name = "DTS_TMP_CLASS")
@NamedQueries({
    @NamedQuery(name = "DtsTmpClass.findAll", query = "SELECT d FROM DtsTmpClass d"),
    @NamedQuery(name = "DtsTmpClass.findByDtsTmpClassId", query = "SELECT d FROM DtsTmpClass d WHERE d.dtsTmpClassId = :dtsTmpClassId")})
public class DtsTmpClass implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @Basic(optional = false)
    @Column(name = "DTS_TMP_CLASS_ID")
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="SEQ_DTS_TMP_CLASS")
    private Integer dtsTmpClassId;
    @JoinColumn(name = "LAP_ID", referencedColumnName = "LAP_ID")
    @ManyToOne(optional = false, fetch=FetchType.EAGER)
    private Lap lapId;
    ...
}

As you can see below, the Lap type implements Serializable!

@SequenceGenerator(name="SEQ_LAP", sequenceName="SEQ_LAP", allocationSize=1)
@Entity
@Table(name = "LAP")
@NamedQueries({
    @NamedQuery(name = "Lap.findAll", query = "SELECT l FROM Lap l"),
    @NamedQuery(name = "Lap.findByLapId", query = "SELECT l FROM Lap l WHERE l.lapId = :lapId"),
    @NamedQuery(name = "Lap.findByDeprecate", query = "SELECT l FROM Lap l WHERE l.deprecate = :deprecate")})
public class Lap implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @Basic(optional = false)
    @Column(name = "LAP_ID")
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="SEQ_LAP")
    private Integer lapId;
    @Column(name = "DEPRECATE")
    private Character deprecate;
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "lapId")
    private Collection<LapAnal> lapAnalCollection;
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "lapId")
    private Collection<LapDomain> lapDomainCollection;
    @JoinColumn(name = "ASSAY_PLATFORM_ID", referencedColumnName = "LOOKUP_ID")
    @ManyToOne(optional = false, fetch=FetchType.EAGER)
    private Lookup assayPlatformId;
    @JoinColumn(name = "LABORATORY_ID", referencedColumnName = "LOOKUP_ID")
    @ManyToOne(optional = false, fetch=FetchType.EAGER)
    private Lookup laboratoryId;
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "lapId")
    private Collection<DtsTmpClass> dtsTmpClassCollection;
    ...
}

What is really strange is that I simply shortened the names of the tables and columns so that Oracle does not limit the limit of 30 characters. It just worked.

I am puzzled!

Thank,

Chris