Now I got further progress! I copied your files and the portable java to the other version of xgm rom builder that I downloaded. Then I can actually build roms. However, when I open the rom to test it in retro arch, there is only a black window.
Thank you! I will also try to ask the person that first recommended the program! :)
I didn't find a way to contact you. If you are open to work for creating original tracks, please get in touch.
Please tell me more! :)