i recently installed bootntr to my 3ds and had to switch to an alternate version of luma. after i realized that this was a mistake i attempted to switch it back to the latest version, specifically replacing the boot firm file.
So you do have the latest Luma3DS (boot.firm) file on the root of the sdcard, and you're encountering this error before it takes you to the home menu?
Try booting into the home menu with the sd card removed from the 3ds.
however i now have come across a new problem which only happens to games that i have changed the region of (my console is japanese) using lumalocaleswitcher:
Do you have a region changed system, that once was Japanese and now it is in NA or EU?
Make sure "game patching" is enabled in
Luma3DS Menu. And re-run
Luma Locale Switcher and check if the desired game is set in the correct region.
Though you still have to give more details on that..