NullPointerException?

[dth]

Hi,

I'm getting this exception:

org.apache.openjpa.persistence.PersistenceException: null
                 at 
org.apache.openjpa.jdbc.meta.FieldMapping.assertStrategy(FieldMapping.java:888)
                 at 
org.apache.openjpa.jdbc.meta.FieldMapping.isEagerSelectToMany(FieldMapping.java:717)
                 at 
org.apache.openjpa.jdbc.kernel.JDBCStoreManager.createEagerSelects(JDBCStoreManager.java:966)
                 at 
org.apache.openjpa.jdbc.kernel.JDBCStoreManager.select(JDBCStoreManager.java:914)
                 at 
org.apache.openjpa.jdbc.sql.SelectImpl.select(SelectImpl.java:867)

Where I'm trying to implement a bidirectional one-to-many mapping via a 
join table:

public class OdsMedarbejder {
...
    @ManyToOne
    @JoinTable(name = "ODS_AFDELINGMEDARBEJDER",
               joinColumns = @JoinColumn(name = "MEDSEQ", 
referencedColumnName = "MEDSEQ"),
               inverseJoinColumns = @JoinColumn(name = "ORGSEQ", 
referencedColumnName = "ORGSEQ"))
    private OdsAfdeling afdeling;
...
}

public class OdsAfdeling {
...
    @Id
    protected double ORGSEQ;

    @OneToMany(mappedBy = "afdeling")
    protected Set<OdsMedarbejder> medarbejdere;
...
}

Any ideas? 

Thanks,

-dennis