WHOOPS, you also need to put this file into the "System" folder in the game folders. Forgot to add that.
Oof... Same exact error message?
I'm currently downloading the folder myself to double-check if everything's okay in there.
Unfortunately I really don't know what could be wrong at this moment. My last resort would be to attempt to launch the game using EasyRPG: https://easyrpg.org/
EasyRPG is an open-source emulator for RPG Maker 2003 games. Sometimes, it can lend a game additional stability - or so I would hope. :(
If this doesn't work either, feel free to request a refund on your purchase. I'm really sorry.