You need to go google Product() as an array vs Range as it confuses the buggery out of me every time I try to use it.

To make it work on the work spreadsheet you need to set the array, can't remember how, or use the vlookup trick of concatenating the key in the target sheet.
There's a way to do a backwards vlookup but forgotten how.

If you study the solution posted by Pecoflyer, you'll see there is no use of PRODUCT(), or array formulae, or VLOOKUP(), because none of them is necessary.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]