Unable to enhance class : x.y.C

Caused by: compile error: remove(x.y.A) not found in x.y.K

@Entity
@Table(name = "a")
@Inheritance(strategy = SINGLE_TABLE)
@DiscriminatorColumn(name = "b_or_c", discriminatorType = DiscriminatorType.STRING)
public abstract class A {
  @Id
  @GeneratedValue(strategy = IDENTITY)
  private long id;

  ...

  @OneToMany(mappedBy = "a")
  private Collection<X> x;

  @ManyToOne
  @JoinColumn(name = "y_id")
  private Y y;

  @ManyToOne(optional = false)
  @JoinColumn(name = "z_id")
  private Z z;
}

@Entity
@DiscriminatorValue("b")
public class B extends A {

  @ManyToOne
  @JoinColumn(name = "l_id")
  private L l;

  @ManyToOne
  @JoinColumn(name = "m_id")
  private M m;

  @ManyToOne
  @JoinColumn(name = "n_id")
  private N n;

}