I downloaded pretendo yesterday, i have the last version of luma and I configurate all, but when I tried to play Mario maker then the game kick me for this error, I tried to play Mario kart 7 but it happens again, I changed my router configuration, i put the DMZ with my 3ds IP and something like uPnP, but don’t work at all.
006-1204 is a NEX Game Server error for the DataStore protocol. This could happen in Mario Maker 3DS as the game is not 100% supported and some features are still missing.
Are you sure you get the same error in MK7? Or a slightly different one? Can you verify the error code in MK7?