Solution : https://service.sap.com/sap/support/notes/817802 (SAP Service marketplace login required)
Key words : 
call function 'gui_upload'    exporting      filename              = l_name      filetype              = 'asc'      codepage = '1100                      <<<<<, sapbwnews bw sp12 netweaver'04 stack 12, 10 content            import support package 20, 0b            import support package 26, external data tab, closing quotation mark, 50            import support package 12, 1 content support package 20, syntax error occurs, file upload program
Related Notes : 
       
| 763340 | SAPBWNews BW Support Package 12 NetWeaver'04 Stack 12 RIN | 
| 723262 | SAPBWNews BW 3.1 SP Content 20 | 
| 723257 | SAPBWNews BW 3.0B Support Package 26 |