merged cells are again the problem. Everyone on this board is saying the same thing - dont use them.

as a test in your file go to cell c1 and type =b1, this will show you want excel 'sees' (0 is am emtpy cell) so at row 21, excel can see that it contiains the merged data and therefore adds 1 to the number above, 22 is empty so it repeats the number above