For some reason, I have a specific cart that doesn't seem to work on the 3DS, no matter what micro sd card I use...but it works fine on the DSi. I tested a separate cart with both microsds, and it works fine no matter what. I do believe it's the specific supercard dstwo cartridge itself, but I'm not absolutely sure. Please advise. Will give info as needed. edit: version of 3DS is 5.1.0-11U , which I think should be compatible.