I tired deleting the preference files last night that did not help. I also ran disk utility as well to no avail.
I think the USB card is overheating. It worked fine this morning for about an hour. Then would not work for more than 5 to 10 minutes. It was very hot when I unplugged it. After it cooled down it was working fine again until it got hot.
Does you card get warm after using it?