HP E4418B Programming Manual page 231

CALibration Subsystem
CALibration[1|2][:ALL]
Error Message
If the calibration was not carried out successfully the error -231, "Data
Questionable; CAL ERROR" occurs. If you are using the HP E4419B the
error message specifies on which channel the calibration failed.
If zeroing was not carried out successfully the error -231, "Data
Questionable; ZERO ERROR" occurs. If you are using the HP E4419B the
error message specifies on which channel the calibration failed.
4-4 HP E4418B/E4419B Programming Guide