How can I fix my Royal 480nt register "EE" error?

You may have lost the programming. If your batteries are old, the memory will be cleared. you will need to get a key which turns to the other positions. First, try a half clear to see if it recovers. if not, you probably need to re-program it.
There is a Royal 480nt programming manual at C-tech:

http://the-checkout-tech.com/manuals/cashregisters/Royal_480nt_user_programming_manual.html

Registerman
May 2012