Cause
This error occurs if your application code attempts to assign a value to an exclusive collection.
When you add a reference to a class and that reference is a collection, it is normally treated as an exclusive collection. The only exception to this is when the reference has no inverse and you explicitly uncheck the Exclusive check box in the Define Reference dialog.
An exclusive collection is inherently bound to its parent object; that is, it is created when the parent object is created and deleted when the parent object is deleted. It cannot be assigned to, and it cannot be referenced from any other object.
Action
Remove the invalid assignment. If the collection has no inverse and you did not intend it to be exclusive, modify it by unchecking the Exclusive check box on the Define Reference dialog. The collection will then be shared; that is, you will have to create the collection before you can use it, and it will be possible to reference it from any number of other objects.