I have a column of dates and a corresponding column of values that are
actually functions converting a foreign currency amount into USD. I want to
create a month-to-date total in a single cell by using SUMPRODUCT. What I am
using is:

=SUMPRODUCT(--(YEAR($A$15:$A$1000)=YEAR($C$7)),--(MONTH($A$15:$A$1000)=MONTH($C$7)),$B$15:$B$1000)

But I am getting the #VALUE! error message. Some of the cells in the dates
array are blank, and there may be a cell in the values array that has an
error because the values are functions themselves. How can I fix this? If I
can assure that none of the cells in the value array have errors will that
make it easier?