SAP Message USMD1040 - Data model &1, entity type &2: Leading entity type &3 is invalid

Diagnosis
Relationships with Leading or Qualifying as therelationship type are not allowed between entity types with thestorage and use type 1 or 2 andentity types with the storage and use type 3.

System Response
The data model cannot be saved or activated.

Procedure
Delete the invalid relationship.