I've been having this problem for the past two weeks now. I had my Acekard 2i for over a year and a half now. But all of a sudden...It stopped working! When I turn my dsi on, it won't be detected it. And when I put it in my old ds lite, It gets stuck on loading screen. My firmware on my Dsi is 4.1U. Can anyone help?
Stuck on loading indicates data corruption. Pop your microSD into your computer and look at your files. Are the file names a jumbled up mess? If so, you'll have to wipe all the data clear and format the card, and then reload it. I hope you've been backing up your saves, you should be doing it once a week if you play relatively heavily.