IBM TN5250 manual Appendix A, You pressed the pad 1 key when it is not allowed

A-6	Appendix A
Table A-4 Status Line Errors, Continued
Error		Description
0019	Dup key not allowed in this field	You pressed the (pad) 1 key when it is not allowed
		in this field.
0020	Function Ctrl key invalid in this field	You pressed a function key that is not allowed in
		this field. Press an escape key sequence (field keys)
		to exit this field, before pressing any more function
		keys or key sequences.
0021	Mandatory enter field, must enter data	The cursor is positioned in a mandatory exit field.
		You must enter data in a mandatory entry field
		before exiting that field.
0022	Status of field not known	A system error occurred. The status of the current
		field is not known. This type of error can occur
		during an insert or delete operation.
0024	Entry not valid in entry field	You pressed a key that is not valid. Only characters
		zero (0) through nine (9) and the (pad) 1 key (if
		specified in the field format word) are allowed in
		this field.
0026	Character entered invalid for this field	You pressed a field key to exit a numeric-only
		field, but the last position of the field will not
		accept a zero (0) through nine (9) character.
0027	Key not defined-key cannot be used	You pressed a key that is either blank or not
		defined for this terminal.
0029	Invalid international character set	The second key pressed in a two-key sequence did
		not produce a valid diacritic character.
0099	Key not valid at this time	You pressed an invalid key sequence.