Your pivot table is showing the same data item two times, effectively treating each instance of the data item as a separate entity. Figure A.6 demonstrates an example of this error.
Figure A.6. Notice that 1/3/2003 is shown in the pivot table twice. There is something wrong here. If these dates are the same, they should be grouped together to give you one calculation, not two.
You are getting this behavior because, although the two data items look the same to you, there is something different between them. Excel is picking up this difference and deciding that they are two different data items. In order to fix this issue, you will have to ensure that the problem data items are exactly the same. Follow these steps to correct this problem: