Solution : https://service.sap.com/sap/support/notes/497101 (SAP Service marketplace login required)
Key words : 
object if_ex_product_customer2~map_r3_to_crm_material, sample source code, material header level, documentation 'customer enhancement, interface method map_r3_to_crm_material, product status 'locked', material exist, product status ', customer namespace, activate interface
Related Notes : 
       
| 872533 | FAQ: Middleware | 
| 623026 | Download R/3 status MARA-MSTAV on CRM distrib. | 
| 495764 | Description of the status in the CRM product master | 
| 428989 | Customer-specific enhancements for data exchange |