When the board booting up, there is a "Kernel Command line". Please check the root filesystem location. it should be something like "root=/dev/xxxxxxxx". For NAND, should be like this root=/dev/mtdblock1.
Is your filesystem store in the SD Card? according to your message, it is looking for the rootfs from the SD Card (mmcblk0) partition 3. Please double check the bootargs in uboot used is correct or not.