CompositionViolationException

Hi,

when I tried to setNamespace() for the second model element, following execption messages always come to me: 

        javax.jmi.reflect.CompositionViolationException
        at org.netbeans.mdr.storagemodel.StorableObject.setComposite(StorableObject.java:251)
        at org.netbeans.mdr.storagemodel.StorableObject.setComposite(StorableObject.java:233)
        at org.netbeans.mdr.storagemodel.AssocEndIndexSet.add(AssocEndIndexSet.java:148)
        at org.netbeans.mdr.storagemodel.StorableAssociation.addLink(StorableAssociation.java:371)
        at org.netbeans.mdr.handlers.AssociationHandler._handleLocalAdd(AssociationHandler.java:155)
        at org.netbeans.mdr.handlers.AssociationHandler._handleAdd(AssociationHandler.java:144)
        at org.omg.library.infrastructurelibrary.core.abstractions.namespaces.AOwnedMemberNamespace$Impl.add(Unknown Source)
        at org.omg.library.infrastructurelibrary.core.abstractions.namespaces.AOwnedMemberNamespace$Impl._add(Unknown Source)
        at org.netbeans.mdr.handlers.InstanceHandler._handleSetR(InstanceHandler.java:166)
        at org.omg.library.uml2.classes.kernel.Class1$Impl.setNamespace(Unknown Source)

I know "CompositionViolationException" indicates that an instance object is going to become owned by more than one element (in sense of aggregation semantics). But I cannot find the exact problem when I examine my metamodel. 

Regards

Fu, Bin