I've been playing through this on my DSI XL with an Acekard. The other day I saved after finishing world 4 and when I went to resume the next day, the game would freeze on the Acekard's loading screen. I tried reseating the card, no change. It seemed like the ROM was somehow corrupted. Other games worked with no issues.
I popped the SD card into my computer, deleted the ROM (left the SAV file) and copied the rom back over to the card from my computer. It works fine now and I was able to pick up where I left off. I've played through a ton of other games on this card and never had this issue, so I'm not sure what happened, but it seems fine now.