@RetroHopeful Not at all. That file only has the settings for the latest controller you configured, no worries :)
It effectively suggests that select is being mapped as the hotkey - which is a good sign!
I'd expect you'd be able to exit a game by pressing the keys you mapped to select and start, together, on the keyboard. And, as you redefine your other controllers, I'd expect you to be able to do the same for each as that happens.
Still, I'm puzzled/concerned with that error message you keep getting - that clearly suggests something is wrong with your current setup.
At this stage, if it isn't too much trouble, I'd strongly suggest formatting your SD card (or trying out a new one), reinstalling the image, and seeing how that goes.