Found your version :p Just bumped into my calc archives and did a binary compare with a Windows XP archive I had of it and it matched. So turns out it is from Windows XP and yes that one works.
Agreed, turns out that it was the one I was using myself too. Until I just swapped it out for calculator plus. The only issue I had was that I wasn't able to setup a keyboard shortcut (Ctrl+Alt+C), but just figured that one out.
Turns out that if you create a shortcut via the send To "Desktop (Create shortcut)" that you can then set it up a keyboard shortcut via properties. As long as your shortcut is on the desktop or in the menu then the keyboard shortcut works. Yay.
But then since it was from xp and not win7 and you didn't know that, does that mean that your calc.exe is something you downloaded off some random site on the net trusting that it didn't contain malware?
So wondering why it would work on your end. Do you have an old .net runtime on your machine perchance?