Solution : https://service.sap.com/sap/support/notes/496404 (SAP Service marketplace login required)
Key words : 
mcod bkup03/feb/02   iii   entering onconfig information correctly26/nov/02   iii   abort, date     section  description-----------------------------------------------------------------------29/jul/03   ii    amending parameters tapedev & ltapedev, generalii  pre-installationiii installationiv  post-installation chronological summary, ======================================================================= iii installation 03/feb/03 entering onconfig information correctlymake, physical logs phase26/nov/02   ii    stop snmp service, ======================================================================= ii pre-installation 29-jul-03 amending parameters tapedev, choose start -> settings -> control panel -> systems2, /instguides -> sap web application server ->release 6, physical logs phasethe installation aborts, ifx_7xkeystyle environment variablebefore starting sapinst
Related Notes : 
       
| 552911 | SAP BW 3.1 Content Server Installation on Windows | 
| 537650 | Informix database versions with IFX_7XKEYSTYLE | 
| 496251 | INST: SAP Web AS 6.20 on Windows - General |