SAP Message USMD1041 - Data model &1, entity type &2: Leading entity types are invalid

Diagnosis
For entity types with storage and use type 3 for which the checktable is predefined by the data element or domain, the other key fieldsin the check table must be mapped using relationships with Leading
as the relationship type. There is not a check table for theentity type, however. No leading entity types can therefore bedefined using relationships.

System Response
The data model cannot be saved or activated.