SAP Message UCF8020 - Characteristic &1 has an ambiguous value in reference document &2; check

Diagnosis The definition of document type &V3& provides a permanent fixing forcharacteristic &V1&. However, this characteristic has no unique valuein reference document &V2&. This contradicts the document typedefinition. System Response Document &V2& cannot be processed. Procedure Correct the definition of document type &V3&.