Hi. Casio TK600 POS has

Hi. I have never heard of a TK600, so I will assume that you are talking about a TK-6000.
Error 1 means you have tried to change modes before finishing in the mode you were last in.
You will need to turn the key back to where you were before, and finish what you were doing. E.g if you were half way through a sale, then turned the key, you would need to go back to REG mode, and press CASH to finish.

If you can't remember what you were last doing, then you will have to flag clear it to stop the current task:

Turn power off at wall.
Turn the key to PROGRAM mode.
Hold down RECEIPT FEED.
Turn the power on at wall.
Wait 5 seconds.
Let go of RECEIPT FEED.
You should see 'FFFFFFFFFF' on the display.
Press SUBTOTAL.
The machine will print out.
Turn the key back to REG mode.
You will need to log a clerk on now (or you will see ERROR 8). So just press a clerk button, or sign on as you normally would.

You should now be able to use the machine.

To reset the sales, turn the key to Z mode. Press CASH. This will reset the usual reports in the machine.

If you have any problems, just let me know.

Mark