Solution : https://service.sap.com/sap/support/notes/550554 (SAP Service marketplace login required)
Key words : 
detail--> application platform--> user interfaces--> sap gui family--> sap gui, html/internet transaction server--> maintenance strategyor directly athttp, sap internet transaction server, --> sap netweaver--> sap netweaver, mouse-click-> view source, sap service marketplace, problems occur frequently, dual host installations, patch level determined, sar solution [1] question
Related Notes : 
       
| 383549 | Patch strategy Internet Transaction Server | 
| 336693 | Replacing or installing librfc32.dll on Microsoft Windows | 
| 335521 | ITS patch installation of kernel files | 
| 331407 | ITS patch installation of SAR packages (IAC packages) | 
| 197746 | Maint. strategy: Internet Transaction Server (ITS) |