I just got my DSTWO an hour ago and I've been trying to get it to work.
First I updated it to the latest firmware. I put the file on my R4, swapped in the DSTWO, pressed B and then updated. It detected it at that point, but not when I boot up my DS Lite with it inside.
I've tried 2 microSD cards, formatted both with panasonic sd formatter. I tried following the beginner setup guide and I put the latest EOS in the root of SD.
What do I do?
EDIT: It did show up once on the 3DS as "Alex Stormrider", but then it gave me an error.