Diagnosis
The object selected for deletion is still being used and cannot,therefore, be deleted.
Entity types: Outgoing relationships, outgoing specicalizations or theentity type are still being used in data models.
Data models: The data model is still assigned to at least one datamodel or is assigned to another model as a referenced model.

Procedure
Double click to go to the definition or hierarchy overview for theaffected objects. From there you can delete the relationships orassignments.
Whan all references have been removed, the object is deleted.