I've had similar problems, but a complete power cycle has always cleared it. Are you sure you powered down the device as opposed to putting it into standby mode?
I have this problem before and after I rooted it. Sorry to say I hated the NC so much now since I spent 5 days messing with it. Wow.. I cannot spend so much more time on it. Please please someone help. I believe I should not keep rebooting every other day