If one or more fields in the PivotTable have calculated items, no fields can be used in the data area two or more times, ...

If one or more fields in the PivotTable have calculated items, no fields can be used in the data area two or more times, or in the data area and another area at the same time. If you are trying to add a field, remove the calculated items and add the field again. If you are trying to add a calculated item, change the PivotTable report so that no field is used more than once and then add the calculated item.