And your DS is on the right firmware? Meaning >11.4? I mean it must be else you couldn't use soundhax. All I can say is that the integrity of the files or your SD card is corrupted, or you just need to keep trying. Other than that, everything should work like it's supposed to.
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Files get corrupted during a transfer often, it's just something that happens when there are too many dropped packets. If you're using Wi-Fi to transfer files to your SD card, do it manually. Also, copy them over more than once to be 100% sure, and check the integrity of your SD card for bad sectors.