Sumproduct formula linking to external workbook works in one file, but not another

Hi FDibbins,

I adjusted the ranges so the are not full columns and now it works! I had known that you shouldn't use full columns with SP, but it worked initially with my first try so I didn't think about it. No idea why it would work in some files and not others, but who cares I can finally move on.

Thanks for your help!