title: SumProduct and VLookup for selected columns
body: <p>I have a function that reads: </p>
  
  <p><code>=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))</code></p>
  
  <p>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).</p>
  
  <p>This returns the <strong>#N/A</strong> error; I am uncertain as to how to rectify this.</p>
  
  <p>I have checked that the names, file paths, rows and columns are correct, and that any hidden rows, columns or tabs are clearly visible.</p>
  
  <p>Any ideas?</p>
  
  <h2>Edit 1</h2>
  
  <p>I have use the "Evaluate Formula" Tool which gives the following results. 
  The first stage in the evaluation yields: </p>
  
  <p><code>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))</code></p>
  
  <p>Stepping into this shows the corresponding date: 6 Apr 2013 (the date in cell D17)</p>
  
  <p>The second stage:
  <code>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))</code></p>
  
  <p>the third stage:
  <code>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))</code></p>
  
  <p>The fourth stage:
  <code>SUMPRODUCT(#REF!+#REF!)</code></p>
  
  <p>The fifth stage:
  <code>SUMPRODUCT(#REF!)</code></p>
  
  <p>And finally:
  <code>#N/A</code></p>