GETPIVOTDATA function only returns zero's
 

I have a pivottable located on a worksheets that is pulling in a access table
and reorganizing it so that i have a subtotal on a particular field.

I am trying to pull the subtotal amount for Store and it is returning 0 as a
value. Here is hte function

=GETPIVOTDATA("dbAmount",$A$3,"dtTransactionDate", DATE(2008,1,25),"strStoreNumber","31137")

I don't know what is wrong with it. the subtotal amount for 31137 should be
make up of two line items for that particular date: row item 1 is null and
row item 2 = 1000. instead of returning 1000 for the subtotal, it returns 0.

Can someone please advise on this.