I don't understand why you would want to invoke a SumProduct formula
with just one condition. Your current formula can be replaced just with:

=SUMIF(SalesDate,AH27,NetSalesHOBO)/100

To also consider a second range to sum with the same condition:

=(SUMIF(SalesDate,AH27,NetSalesHOBO)+SUMIF(SalesDa te,AH27,VATHOBO))/100

John wrote:
I am trying to add the Range Name - VATHOBO to NetSalesHOBO to the existing
formula below, but can't get the syntax correct. Perhaps someone could help


=IF(ISERROR(SUMPRODUCT(--(SalesDate=AH27),NetSalesHOBO))/100,0,SUMPRODUCT(--
(SalesDate=AH27),NetSalesHOBO))/100