Solution : https://service.sap.com/sap/support/notes/517589 (SAP Service marketplace login required)
Key words : 
/400 single_execution rz12 sccl scc9 reason, basis support package versions, set dbs/db4/use_hints, sap basis system version 4, sap basis system version 6, remote client copy process, remote client copies, lib_dbsl patch level 1105, sap system release, kernel patch level 969
Related Notes : 
       
| 541311 | CC-INFO: Parallel processes FAQ | 
| 540158 | iSeries: Error -901 in client copy | 
| 446485 | CC-ADMIN: Special copying options | 
| 212727 | CC-INFO: FAQs for parallel processes up to Release 4.6D | 
| 208919 | CC-INFO: Performance as of Release 4.6 | 
| 206523 | CC-RELEASE: Client copy errors in 4.6C and 4.6D | 
| 92589 | AS/400: TCP/IP Read/Write buffer > 1 MB |