Solution : https://service.sap.com/sap/support/notes/799082 (SAP Service marketplace login required)
Key words : 
sapbwnews bw sp11 netweaver'04 stack 11, runtime error getwa_not_assigned occurs, 10 content            import support package 20, 0b            import support package 26, field symbols <l_sx_ff>, internal business volume, constant selection reason, 50            import support package 11, 1 content support package 20, 0b support package 26
Related Notes : 
       
| 794721 | GETWA_NOT_ASSIGNED in SAPLRRK0; subrout. CHECK_NAV_INIT_BACK | 
| 763338 | SAPBWNews BW Support Package 11 NW'04 stack 11 RIN | 
| 723262 | SAPBWNews BW 3.1 SP Content 20 | 
| 723257 | SAPBWNews BW 3.0B Support Package 26 |