What's the difference? Why my method is not working?
Because your original MK7 .sav file will not work alongside the .3DZ conversion, that was meant for the original .3DS rom, it creates a different size .sav file on your SD card which will corrupt when you start the new .3DZ conversion MK7 game, it does not recognize the original .sav file. Gateway are going to try to crack in the next FW update. I hope this helps you