Making a sum from two totals on a report

[crashe]

I have been 'voluntered' to do a tuition program for my son's high school. It involves charges to the students and records payments. I have it about ready, but in the account report I can't get a grand total from the charges less the payments.

In detail: I have the itemized charges in the report with a total. I used a sub-report to detail the payments with a total. I placed this in a footer. I want to get a grand total (charges less payments) to the account footer but come up with "name?" errors mostly. Can someone lend a hand so I can get my life back?

Thanks!

 

[Smack]

Not sure if this will help.....
I have a form with a subform that shows credits paid (Credit Amount) there can be multiple entries for a single record. Create my report, I used a query, and used the sum function for credit amount. When this field was placed on my report it was named SumOfCreditAmount. On the report footer, I then used =Sum([SumOfCredit Amount])
Hope this helped.
-Smack