Solution : https://service.sap.com/sap/support/notes/586597 (SAP Service marketplace login required)
Key words : 
system generates error message iw006 ', pm planning plant', iw006 reason, plant maintenance, incorrect plant, maintenance order, bapi bapi_alm_order_maintain, terms bapi_alm_order_maintain, solution implement, program correction
Related Notes : 
       
| 736204 | Notes for downgrade kit ALMBAPI I | 
| 708508 | Downgrade BAPI_ALM_ORDER_MAINTAIN -> errors |