yeah acekard (official firmware atleast) will play my R4 saves (just bought an acekard2).
i had to rename them from .SAV to .nds.sav (note the case) for the official acekard firmware.
but i also back up all my sav's to my PC and you should too
this happened to me. i returned mine to where i bought it and they replaced it . i tried everything - different DS's, different microSD cards, different firmware. still crapped out.
good luck