RRRRRRG.

So I was gonna do some work on my scenario today.
Was.

And then.

"ERROR: Could not locate Civilization III: Play the World. Please make sure the game has been properly installed and try again."

In spite of.
The game working fine. And being exactly where it should.
The folders being fine. And being exactly where they should.
NOTHING, even remotely, having changed. Absolutely zilch. I did nothing, changed nothing, made no alterations whatsoever.
But the editor which I edit the scenarios in.
Can't find the game!
In spite of it.
Being in a folder.
INSIDE OF THE GAME.
It literally has stopped finding something which it wouldn't be able to exist without.

​I'm pretty miffed.