Hey TenshiHanka!
Have you installed the RPG Maker 2003 Run Time Package? RPG Maker 2003 need it's default template files in order to function. :(
https://www.rpgmakerweb.com/download/additional/run-time-packages
Alternatively if this doesn't work, there's this project called EasyRPG which is meant to port RPG Maker 2003 games over to other platforms other than Windows PC. You can install a windows executable file from the link below and the move into the game file folder.
https://easyrpg.org/player/downloads/
Next time I release another RPG Maker game I will make a version with the RTP included.
I apologize for this inconvenience but I am thankful you are willing to try out my game.