????????????
I dont want stress you, but is need.

This is your code. Run and see.

CREATE TABLE MyTable (MainKey C(6),No_in_row I)
INSERT INTO MyTable VALUES ('JKT001',                     10)
INSERT INTO MyTable VALUES ('JKT001' ,                    20)
INSERT INTO MyTable VALUES ('JKT002'  ,                   10)
INSERT INTO MyTable VALUES ('JKT003'   ,                  10)
INSERT INTO MyTable VALUES ('JKT003'    ,                 20)
INSERT INTO MyTable VALUES ('JKT003'     ,                30)
INSERT INTO MyTable VALUES ('JKT003'      ,               30)
INSERT INTO MyTable VALUES ('JKT003'       ,              40)
INSERT INTO MyTable VALUES ('JKT003'        ,             40)

select MainKey, ;
      IIF(count(*) > 1, "Yes", "No ") AS Duplicate,   ;
      IIF(count(*) = 1, PADC("N/A",10), PADL(No_in_row,10)) AS No_in_row   ;
  from MyTable;
  group by MainKey, No_in_row ;
  into cursor crsDupsTemp
SELECT * ;
	FROM crsDupsTemp ;
	GROUP BY MainKey, Duplicate, No_in_row ;
	  into cursor crsDups

ON crsDups, row n° 3 have this values.

JKT003                      No                   N/A

Your code can to be write on a single query:

select DISTINCT MainKey, ;
      IIF(count(No_in_row) > 1, "Yes", "No ") Duplicate,   ;
      IIF(count(No_in_row) = 1, PADC("N/A",10), PADL(No_in_row,10)) AS No_in_row   ;
  from MyTable;
  group by MainKey,No_in_row;
  into cursor crsDups

Fabio