Kobo Desktop 3.9.0 install problem

I've seen two reports that Desktop 3.9.0 is being rejected by Windows with the following error message: C:\Program Files\Kobo\Kobo.exe is not a valid Win32 application.

I'm not sure what's happening, I installed it just fine into Windows 7.

One of the reports had a problem installing onto Windows XP.

I'm creating this thread so there's a central location for the discussion of the probable problem.