Like, I don't know what to do, there's so much crap happening.
Hi L & R Buttons, that's very strange, could you maybe try clicking "Build Options" and selecting "Empty Build Cache" from the menu, and trying to build again? I'm wondering if it's compiled a file incorrectly and is stuck using a cached version of that file for some reason.
The other thing you could try is going into your temporary folder (which you can find in the application preferences)
If you open that folder it will contain "_gbsbuild", "_gbstools", and "_gbscache". Try deleting all three of these folders, restarting GB Studio and trying to build again.
Please let me know if either of these methods fix the issue for you as it will help me track down what could have happened to prevent the problem for others in the future.