Hi Dan!
I wrote up the steps you need to use to get the desired results.
1. Go into Report Writer (Tools | Customize | Report Writer | Choose the Reports Button) and open the Invoice Form
2. Click on the Sort button on the Report Definition window.
3. Insert the following sorts in this order:
Invoice Number from the InvoiceTransaction Work file
Item Class Code from the Item Master file
Note - To have Item Class Code insert under the Invoice Number, first highlight Invoice Number and then insert the Item Class Code.
4. Click OK to save the sort.
5. Click on the Layout button on the Report Definition window.
6. Under Tools on the toolbar, select Report Section Options.
7. In the Additional Footers section, highlight the footer Comment 4 and click New. Highlighting Comment 4 before clicking New will insert the new footer under the Comment 4 footer, NOT above the other footers.
8. Title the footer Item Class. With the Report Table as Item Master, select the field Item Class Code. Also un-mark the footer option Suppress when field is empty. Save the new footer. This will be our subtotal field.
9. Select the footer "Invoice" (it should be right below the one we just created in the list) and click open. Change The Report Table to "Invoice Transaction Work" and choose the field Invoice Number. This will prevent our page from breaking after each class. Click OK and close the Report Section Options window.
10. From the Toolbox, select the Invoicing Transactions Amounts Work table. Drag out the field Extended Price into the new footer (which should be F2).
11. Double click on the field and change the type to Sum.
12. If you also want the Item Class to print on the report, pull out the field Item Class Code from the Item Master file into the F2 section.
13. Save the report layout and save the report also. Return to Dynamics (File | Great Plains Dynamics).
14. Remember to grant security to the modified report (Setup | System | Alternate/Modified Forms and Reports).
The above should get the report how you want it to look. If you need further assistance with the above steps I would recommend opening a support case with the GP support team and reference this forum page.
Thank you very much for your time and have a great day!