I will echo the sentiment of others here in that you should always use good, reputable SD cards. Worth every penny and makes a big difference.
indeed, the memory card is not a place to skimp. that said, in the original post, he said that he was using a SanDisk Ultra. SanDisk is one of the best companies making flash cards, and the Ultra line should be fine. it's possible that he has a fake SanDisk card (particularly if he bought from ebay), but the SanDisk Ultra cards are great cards. and he says that they are relaitvely "slow" at 15 MB/s.
Two channels of 24/96 PCM audio is only 0.55 MB/s. If you double that to two channels of 24/192 audio data, that is still only 1.1 MB/s. heck, even if you double that again for 4 channels of 24/192 audio, you're only at 2.2 MB/s. My point is that all of this is well below the stated spec of the SanDisk Ultra card of 15 MB/s.
Based on this, assuming it's a genuine SanDisk card (and assuming the card itself is not malfunctioning), I would guess that there was some other cause behind the drop-outs, and it's not a simple matter of the "card not being able to keep up".