Solution : https://service.sap.com/sap/support/notes/621783 (SAP Service marketplace login required)
Key words : 
system issues error am006, terms am006 reason, upload sales transactions, error occurs, reference missing, assignment person &, company address &, relevant scenarios, data exchange, reference fields
Related Notes : 
       
| 641910 | Download to CRM: Dump GETWA_NOT_ASSIGNED (2) | 
| 634820 | Downloading into CRM: GETWA_NOT_ASSIGNED dump |