Strange calculation problem

[potts]

I have created a report with two subreports. These are all linked by a CustomerID. The subreports contain subtotals that are needed for the calculation of the grand total (an unbound text box using an expression for the calculation) on the main report. In general the grand total calulation works fine. That is until I print reports for multiple customers (I have a form for this that permits you to print multiple records from a list box selection). What happens in this case is that the sub totals in the subreports for the first report are added onto the the grand total for both the first and second reports. This does not happen if you print them one at a time and I just don't understand it.... does anyone else?

Here's the calculation code:

=IIf(IsNumeric([SubAccessFee])=True,[SubAccessFee],0)+IIf(IsNumeric([tblCustomer].[Report]![SubSupFee])=True,[tblCustomer].[Report]![SubSupFee],0)+IIf(IsNumeric([Invoice1Charge].[Report]![SubChargeFee])=True,[Invoice1Charge].[Report]![SubChargeFee],0)+IIf(IsNumeric([Invoice1Prog].[Report]![SubProgFee])=True,[Invoice1Prog].[Report]![SubProgFee],0)