Solution : https://service.sap.com/sap/support/notes/521961 (SAP Service marketplace login required)
Key words :
issue message 00347 'field ekpo-ematn, mass maintenance purchase orders posts, change field ekpo-ematn, change field massekpo-ematn, mass maintenance purchase orders, massekpo-ematn field, field massekpo-ematn, prerequisites program design, mass maintenance memasspo, call transaction me22