If the game is out of region, try one from your region, or try this "If the WUD is USA, for EU console, in the "content\LuigiBros\msg" folder, "USA_en" must be renamed to "EUR_en", as well as in the folder "content\LocalizedData", "UsEn" must be renamed to "EuEn", in order for the game to boot. If the WUD is EU, for USA console rename the folder EUR_en to USA_en and EuEn to UsEn."I found a mini partition maker thingie on the web, should i use that?
Try another download of the game.
Try another SD card.
Try enabling the log server with the IP of your PC, run the log server on your PC (loadiine_server.exe) then run the game and look at the log output to find out what's wrong.
Other than that, I don't know.