I probably should have spoken up sooner about this. sorry.

The problem is related to the fact that, in Magritte3, you have to instantiate a class before you can access its description. 

MARelationDescription>>reference attempts to get the description of the class returned by MARelationDescription>>commonClass. But the commonClass is MADescription and instantiating it fails because it is "abstract". You could change MADescription>>isAbstract to return true and it should work but that could break something somewhere else. (I do not have an image handy with Magritte3 installed or I would try it myself). Otherwise, have a look at MAReferenceDescription class>>descriptionReference and you will notice that it builds its classes from MADescription allConcreteClasses. This is what causes the commonClass method to return MADescription. Perhaps changing the base class to MAElementDescription might work?

John