: Perform a cleanup of old WinCC Flexible installations. Follow the official Siemens guide: What can cause the installation to abort or prevent successful starting of WinCC flexible?

Right-click on the Setup.exe file and select "Run as administrator." This is a mandatory step to ensure the installer has the necessary permissions.

Once you have securely downloaded the ISO image or ZIP file containing WinCC Flexible 2008 SP3, follow these steps for a clean installation inside your supported environment (or VM): Step 1: Extract or Mount the Files