What's happening is exactly what your SSH client says. You already had an host key saved for this specific IP, and the one on your Kindle is different, so your client is shouting at you, because that could be VeryBad(TM) is we were talking about anything other than a Kindle

.
If you're sure this previous host key isn't important, you can remove it from your ~/.ssh/known_hosts file.
Also, I wouldn't SSH from root, ever.