Many Sharp cash registers such as the Sharp ER-A410, ER-A520, and ER-A530 offer clerk functionality, allowing you to track net sales for individual employees. Even if you do not use separate clerk logins, machines that have clerk functionality require that at least one clerk must be signed on in order to use the cash register. Most often, this is just CLERK 1.
The NOT ASSIGNED error generally means that there is no clerk signed on to the machine. Clerks can be signed off by pressing a combination of buttons, or they may be signed off after making system programming changes. To sign the default clerk back on, you would press number 1 on the number pad keys (usually gray in color), followed by a button that may say SERV #, CLK, or CASH #. After doing this, the display usually will read -0001- indicating that CLERK 1 is now signed on and you should be able to resume using the cash register.