Blue Arrow on my screen

In K5 you have

=COUNTIF(K7:K3994, "<>")

and in K9 you have

=IF(AND(K5=K6,K6=K7),"OK","Error")

K9 refers to K5 in an equality test, and K5 refers to K9 for a content test. That's circular. Can you rewrite the K5 formula to look only at the cells you really need to evaluate? From this sheet it is not at all clear what you are looking for in that COUNTIF, since there is no data or formulas past row 9.

Edit: The same problem occurs in multiple columns.