Solution : https://service.sap.com/sap/support/notes/127071 (SAP Service marketplace login required)
Key words : 
symptom additional key words business area, additional key words direct input, activate business area balance sheets, additional key words rwin, business area balance sheets, customer/vendor line items, business area exists, unique business area, customer line item, business area
Related Notes : 
       
| 1490708 | Business area in the customer line item | 
| 125082 | SD-FI: Business area missing in customer item |