I had that happen to me once on one of my HD's. Turning off wifi followed by a full power down and restart fixed the problem.
I have not had this problem but you could try going into settings/all settings/apps/nook keyboard and clear the cache and data also force stop but you will need to shut down and turn back on if you do that.
Maybe a soft reset will work as well. Hold power button down until it shuts off(20 seconds approx) then turn back on.
Last thing would be to try to download a new keyboard from the Play Store. There are some free ones out there.
Good Luck and keep us updated Maybe a call to B & N might help as well. You never know.