Solution : https://service.sap.com/sap/support/notes/946204 (SAP Service marketplace login required)
Key words : 
dimp order type lop, long products planning, prerequisites alternative units, 1st order item, alternative units, order item, -products reason, production order, order items, item quantity
Related Notes : 
       
| 731290 | Current release restrictions for ECC DIMP 5.0 |