Hmm... Make sure you have Luma3DS 9.1 Plugin Edition installed on your console. If not, copy the file "boot.firm" to the root folder of the console. If it still doesn't work, move the plugin to the folder:
/luma/plugins/<TITLEID>/<filename>.3gx
MK7 TITLE ID:
Taiwan: 000400000008B400
Japan: 0004000000030600
USA/Americas: 0004000000030800
Europe: 0004000000030700
Europe [UPDATE 1.1]: 0004000E00030700
To activate the plugin, go to Rosalina Menu > Plugin Loader: and turn the [Enabled] option. For use the cheat menu in MK7, use "SELECT" 3DS button.