From here
The page footer and header sections, however, do not support calculated controls that use aggregate functions such as Sum
You can however use VBA to calculate page aggregates. The linked MS article explains how. The summary of their instruction is this:
Private Sub Detail_Print(Cancel As Integer, PrintCount As Integer)
If PrintCount = 1 Then
txtPageSum = txtPageSum + ExtendedPrice
txtPageQuantity = txtPageQuantity + Quantity
End If
End Sub
Access increments [the PrintCount] property by one whenever the data for the current section is printed. Because there are times when the Print event for the Detail section for a particular record might be called more than once, checking the PrintCount value ensures that you don't add the same value twice to a page total.
Reset the numbers for the next page print
Private Sub PageHeaderSection_Print(Cancel As Integer, _
PrintCount As Integer)
txtPageSum = 0
txtPageQuantity = 0
End Sub
Again, see the MS help page for more details.