This is usually caused by wear or liquid contamination in the keyboard membrane which is located at the bottom of the keyboard and looks a little like this:
http://velesoft.speccy.cz/samcoupe/keyboard/samcoupe-membrane-full.jpg
----------------------------------------
If anyone needs a Royal 600 / 601 manual, go here:
http://the-checkout-tech.com/manuals/cashregisters/royal1.php
Registerman
July 2010