Chosen Solution
I have a copy of New Super Mario Bros. that loads just fine on my DSi XL but won’t load on my New 3DS XL. It detects the game, but when it loads it says that an error has occurred. The 3DS loaded my copy of Pokemon Black just fine. I’m going to continue trying things to see if I can get it to work properly, but if anyone knows of anything specific that could be causing this issue, I’d appreciate a solution.
The game cartridge could be damaged or have dirt inside it. Try cleaning it with a slightly damp cloth..
