SATO CT4-LX Operator's Manual page 479

Error Message 1020 (Calendar Error)
When there is an error with the product, the error message appears on the screen.
Tap the error number button to show the details screen.
Check the cause and countermeasure, and then take appropriate action.
To clear the error:
Tap [SETTINGS] to change the calendar settings, or tap [CLEAR], or power off the product.
Cause and Countermeasure
Cause (1)
The date and time of the calendar are
incorrect.
Countermeasure (1)
Set the calendar again.
Cause (2)
The battery for the calendar is running low.
Countermeasure (2)
The battery for the calendar needs to be
changed. Contact your SATO technical
support.
Reference
Regional
Contact Information for When You Are in
Trouble
479