Solution : https://service.sap.com/sap/support/notes/861360 (SAP Service marketplace login required)
Key words : 
property business partners, sap business partner, bp000-partner field, business partner conversion, business partner, bp000 table, report rftbup10_bp000, consistency check, unique assignment, selection screen
Related Notes : 
       
| 858123 | BP_TR2: Table BP000 is deleted by RFTBUP10_BP000 | 
| 762061 | BP_TR2: Deactivate consistency check for table BP000 | 
| 398888 | BP_TR1: Composite note and FAQs about bus partner conversion |