I have a DSi and DS lite and the Acekard 2i fits in fine in the DSi but not on the DS lite. It goes in but it just doesn't click and stay down. I push the cart all the way down and it pops right back up. I don't think it has to do anything with the DS lite because other original game carts work just fine.
I would suggest exchanging the acekard. Take out one of your retail carts and compare the size. The makers of acekard have no idea what they're doing in terms of hardware, it doesn't even come close to the real size of a ds cart. Mine fit, and it still didn't match up in size. Yours is likely even smaller than mine because they don't know how to build them, so it just isn't pushing down far enough to snap in.
