Ensure you have the legitimate SIMATIC_WinCC_flexible_2008_SP5.iso (typically around 3.5 GB). Do not confuse it with WinCC Flexible 2008 China Edition or WinCC Flexible 2005.
: WinCC Flexible 2008 SP5 was officially released for Windows XP (SP2/SP3), Windows Vista, and Windows 7 (32-bit). It was never validated or supported by Siemens on Windows 10. However, many industrial facilities still operate legacy HMIs that require this software for maintenance, modification, or migration.