SumProduct and VLookup for selected columns

Question

I have a function that reads:

=SUMPRODUCT(VLOOKUP(D17,'D:\Temporary Storage - not backed up and unsecured\[PT current plan.xls]Ore Fines'!$A$12:$BC$146,{4,8,12,16,20,24,28,32,36,40,44,48,52},FALSE)+VLOOKUP(D17,'D:\Temporary Storage - not backed up and unsecured\[PT current plan.xls]Lump Ores'!$A$12:$AY$146,{4,8,12,16,20,24,28,32,36,40,44,48},FALSE))

The aim is to look for the matching date (Column D) in each relevant tab, then add up the cells corresponding to a column heading of "usage" only (the column heading repeat every 4 cells).

This returns the #N/A error; I am uncertain as to how to rectify this.

I have checked that the names, file paths, rows and columns are correct, and that any hidden rows, columns or tabs are clearly visible.

Any ideas?

Edit 1

I have use the "Evaluate Formula" Tool which gives the following results. The first stage in the evaluation yields:

SUMPRODUCT(VLOOKUP(41370,'D:\Temporary Storage - not backed up and unsecured\[PT current plan.xls]Ore Fines'!$A$12:$BC$146,{4,8,12,16,20,24,28,32,36,40,44,48,52},FALSE)+VLOOKUP(D17,'D:\Temporary Storage - not backed up and unsecured\[PT current plan.xls]Lump Ores'!$A$12:$AY$146,{4,8,12,16,20,24,28,32,36,40,44,48},FALSE))

Stepping into this shows the corresponding date: 6 Apr 2013 (the date in cell D17)

The second stage: SUMPRODUCT(#REF!+VLOOKUP(D17,'D:\Temporary Storage - not backed up and unsecured\[PT current plan.xls]Lump Ores'!$A$12:$AY$146,{4,8,12,16,20,24,28,32,36,40,44,48},FALSE))

the third stage: SUMPRODUCT(#REF!+VLOOKUP(41370,'D:\Temporary Storage - not backed up and unsecured\[PT current plan.xls]Lump Ores'!$A$12:$AY$146,{4,8,12,16,20,24,28,32,36,40,44,48},FALSE))

The fourth stage: SUMPRODUCT(#REF!+#REF!)

The fifth stage: SUMPRODUCT(#REF!)

And finally: #N/A

Answer 1

Wrap SUM() around the VLOOKUPs:

=SUMPRODUCT(SUM(VLOOKUP(D17,'D:\Temporary Storage - not backed up and unsecured\[PT current plan.xls]Ore Fines'!$A$12:$BC$146,4,8,12,16,20,24,28,32,36,40,44,48,52},FALSE))+SUM(VLOOKUP(D17,'D:\Temporary Storage - not backed up and unsecured\[PT current plan.xls]Lump Ores'!$A$12:$AY$146,{4,8,12,16,20,24,28,32,36,40,44,48},FALSE)))

When you have arrays of different sizes, when both are larger than one element long, you will get an error, for example:

=SUMPRODUCT({1,2}+{1,2,3})

Will give an error because the arrays are not of the same size. A quick fix is the SUM():

=SUMPRODUCT(SUM({1,2})+SUM({1,2,3}))

Which adds up each element in the arrays first.