Solution : https://service.sap.com/sap/support/notes/676073 (SAP Service marketplace login required)
Key words : 
general ii     pre-installation iii    installation iv     post-installation chronological summary, documentation 'installation guide - sap web application server abap 6, date      section  description --------- -------  ---------------------------------------------------20/mar/06  iii      missing dlls, dll module=ciantregistryentriesthe subkey 'hkey_users\s-1-5-21-299502267-1958367476-725345543-1206\ environment', copy registry branch 'hkey_users\s-1-5-21-299502267- 1958367476-725345543-1206\environment', ii     pre-installation 09/oct/04ecc 5, iii    installation 20/mar/06missing dlls, mscs installation09/oct/04  ii       ecc 5, node b09/oct/04  iii      error, iv     post-installation
Related Notes : 
       
| 728879 | MaxDB: MSCS installation based on Web AS 6.40 | 
| 723288 | Central Installation Note SAP Web AS 6.40 SR1 | 
| 674522 | SAP Web AS 6.40 Installation on Windows: Informix | 
| 539523 | DB6: MSCS Installation on IBM DB2 UDB for UNIX and Windows |