Another Excel user states that this equation works on his computer

=SUMPRODUCT(IF(C10:C21<1099.41-F10:F21,C10:C21,1099.41-F10:F21),M10:M21)

However, when I formula audit - it gives me a value error on the first
c10:c20.

I know that all my values are good. If I remove the "IF" I can get an
answer - again just confirming that it is not a problem with the data. I'm
using v. 2003

Any ideas