Hi. Error 99 (or EE-99) usually indicates loss of program. Normally caused by battery going flat (if left unplugged for too long). You need to re-program it. Checkout tech has the programming manual for this model:
https://the-checkout-tech.com/manuals/cashregisters/Uniwell1.php
Try just programming one or two things on it first, then power it off overnight. If it goes back to error 99, your battery is no good.
Registerman, April 2018
