Kindle Fire error: "Unexpected error:Null"

Armelline

I've successfully published my first game to the Kindle store (hopefully Pro account coming soon!) and went to submit my second. However, when testing it on the emulator, I get a weird error. As the app loads, while still on the custom loading screen, this error comes up:

Unexpected error:Null

This game has very simple logic on the first scene and this error still occur with the two if statements stripped out. My previous game was far more complicated (though still pretty simple) logically on the first scene.

This error occurs on all the Kindle versions I've tried on the emulator.

To be clear - my other - more complicated app works just fine so it seems unlikely it's a problem with my setup. I'm guessing it's something iffy in my "code".

Anyone encountered this?

Edit: Okay, so for a second time I reinstalled the emulators, republished the app, re-installed it on the emulators. As far as I know I did nothing different to the first two times I tried. But this time the game is working, so never mind I guess. Just wish I knew what had changed things to make it work