I'm having the same issue as the original poster, getting the "not a valid win32 application" message using the latest portable download on Windows XP. The admin saying "works for me" is incredibly unhelpful in troubleshooting this problem.

@doug526: What is "XP 32 bit legacy"? The current latest version of WinSCP application (6.1.1) works on Windows XP SP2 32-bit.
https://winscp.net/eng/docs/requirements#client

Can anyone specify the latest version that works in XP 32 bit legacy? Current portable download says it is not a valid win32 application.

Yes it will work on 32 bit OS

As you have found out meanwhile, on old versions of Windows, you need to use the "Portable executables" download:
https://winscp.net/eng/docs/requirements#client

Hi there

Due to several reasons, i still use Windows Server 2003 (no R2) 32 Bits for some special applications.

Question: Most current version WinSCP-5.17.10-Setup.exe does not; which one is the last version that does?

I get a message when i start the installer: " ... is not a valid Win32 application"

But i WinSCP is only available in a 32 bits but not in a 64 bits version. Maybe i'm wrong with that. (???)

Before i used WinSCP-5.13.8-Setup.exe, and that was working.

Thank you very very much for your feedbacks!! :-)

With kind regards from Switzerland,
Jan