This usually occurs because of filler. For example:
01 my-record.
03 my-key.
05 filler pic xx.
05 field-1 pic xx.
If my-key is declared as a record key, this error occurs because the area of the key described by filler is not included in the XFD.
Resolution:
To correct this error, ensure that every character that is part of the key is included in some field that is part of the XFD. Use an XFD to give a field name to each filler, to ensure that fillers are included:
01 my-record.
03 my-key.
$xfd name=myfiller
05 filler pic xx.
05 field-1 pic xx.