You know, I think I might have just spotted something. We have roaming profiles here, and in my C:\Program Files\ScreenShotCaptor directory, I have a 'servername' directory. In there, I have "users$", my account name, My Documents, DonationCoder, ScreenshotCaptor, and then a Screenshots directory. This is on a clean install. That looks quite unusual to me.
And it will run in portable mode....
but it won't run with the ConfigDir INI set to %MYDOCUMENTS% (which was commented out)
but it will when it's set to %PROFILE%
I think I got it. The extra directory you called out above gave me the idea for the fix.