Assuming you've done the referencing correctly, the formula will work BUT you will need the source workbook to be open for the formula to return a result. That's quite possibly why you're getting the "N/A" errors. You can get around that by creating a reference sheet in your target workbook that explicitly references each cell in the source workbook, then point the formula in your target workbook to that new sheet (which can be hidden and protected, if needs be).

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]