Solution : https://service.sap.com/sap/support/notes/897804 (SAP Service marketplace login required)
Key words : 
/    important general information            ii/   tasks prior, mysap crm server landscapeyou executed, client copy            iii/  errors, client copy            vi/   actions, crm server client, crm release independent, related notes section, guide            iv/   additions, client copy procedure, client copy wizard
Related Notes : 
       
| 585725 | Incorrect system release determined for R/3 site | 
| 577778 | Postprocessing after client copy | 
| 564435 | Additional information on CRM System copy | 
| 519488 | logsys corrections for enabling the 'BDLS' tx conversion | 
| 457707 | Change of the back-end system | 
| 445195 | CC ADMIN: Remote copy with cross-client Customizing | 
| 418886 | Download: Products not found or not changeable | 
| 103228 | Naming the logical system | 
| 24853 | CC-INFO: Client copy, functionality |