Can someone help me with why this formula is returning a #NA?

=IF(SUMPRODUCT((Revisions!$C$3:$C$410=$B5)*(LEN(Revisions!$F$3:$F$411)=0)),"Y","")


Essentially what I'm trying to do is look at the Revisions tab, and if at any spot where column C (Revisions Tab) has the same contract number as $B5, and all cells in "F" (Revisions Tab), marked with a "Y", then it would say "Yes" - meaning we have received all revisions. If there is a blank value in column F, or a "N", it would say "No". Indicating not all revisions are returned.