Do you have a card in both slots? When I did this on my n810 the labels for the internal and external cards would switch when booting and then switch back after booting. To fix this I had to add an entry to the boot menu to boot from partition 2 of what would normally be the external card. This was discussed back on page 5 of this thread for more info on what to do if this is your problem. If you do have two cards in try booting with only the internal card in first to see if that works.