Try formatting the game, start the game up and press and hold a,b,x,y at the same time during boot. Then erase the save data when asked. Then use the latest version of fbi installer 2.3.1 and inject the 2 files into the game then load the game up and try again.Can't seem to get this to work on my US N3DS XL. Injected the save using JKSV, but when I try to load up the payload, the game crashes and 3ds prompts me to restart the system.
Don't forget the boot.3dsx Homebrew loader file on the root of the sd card.