There's another possiblity to this problem that I don't think anyone has mentioned yet
USA DSi Firmware update has
blocked Acecard 2i (& possibly others like the DSTTi)
From what I've read so far is Japanese firmware end in 'J', Europe ends in 'E' & 'USA' ends in 'U' (e.g. 1.3J,1.3E,1.3U)
Although I know (from experience) that 1.3E firmware works with both DSTTi and Acekard 2i (I have both), could it be that USA firmware is blocking them ?? or perhaps JUST the Acekard
What we need to know is what firmware the (USA) DSi has installed.
If someone has a 1.2U (or whatever) & the Acekard works - then we find someone with a 1.3U & find it doesn't (making sure it's the same type of Flash card), then this does point towards firmware update blocking. It may be the update is also only blocking certain cards (perhaps just the Acekard)
What's really needed is a 'flashcard work/don'twork survey thread' so I've started one at
http://gbatemp.net/index.php?showtopic=146321