My formula is like that as followed:

=COUNTIF(OFFSET(AF:AF, 11,0,128,1),"TRUE")

And I got a result as "0". Then I evaluate the formula, it showed
"Countif($AF$12:$AF$139, "TRUE") ". This is exactly what I want.

Then I tried to type "Countif($AF$12:$AF$139, "TRUE")" into a cell, it came
up with the right answer.

So I don't know what I did wrong in the original formula?