how can i clear my problem ?

"NOT ASSIGNED" means you have not logged on to the machine. try this:

Press clear (CL) then press 1 then press CLK# button. On some models this is called CASH# button. It is at the top of the keyboard.
Now try the machine.

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If anyone needs an XE-A303 manual, try here:

http://the-checkout-tech.com/manuals/cashregisters/Sharp_XE-A303_programming_manual.html

Registerman
November 2010