That was happening to me until i ran mkfs.vfat on the first partition of the 3 partitions that the guide tells you to make (so something like sudo mkfs.vfat /dev/mmcblk0p1). The guide doesn't explicitly say that this is required (it only mentions running mkfs.ext3 on /dev/mmcblk0p3), but after I did that it worked (I also reflashed the kernel after doing that, but I dont know if that's required).

Let me know if I can help any further!