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.
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.