Also check for Misc charges on the invoice. Basically, any table that has records and that links to InvcDtl could be duplicating your total. Check out the Report Data Definition to see the Report Relationships and Data Sources.
You may want to consider writing a Subquery in the ARForm Select Statement to sum the quantity.
Epicor is doing some VB magic in the background because the invoice is typically printed as a Group (with many invoices). I have struggled with this before and found it was just as easy to add a subreport in the RDL Select statement.
i.e.
(Select SUM(T100.SellingShipQty) FROM InvcDtl_" + Parameters!TableGuid.Value + " T100 WHERE T2.Company = T100.Company AND T2.InvoiceNum = T100.InvoiceNum AND T2.InvoiceLine = T100.InvoiceLine) AS InvcDtl_SellingShipQty
Disclaimer: I have not tested this - just scratched it out.
DaveO
I would try and pinpoint when the value gets doubled. Is it on invoices with more than 1 line, is it invoices with misc charges, etc. My guess is that it happens intermittently because the majority of invoices have an empty table.
I was asking about changes because I have seen instances where a join gets duplicated by accident.
Mr. Shawn: try removing the reference to the Iinvoice line.
i.e.
(Select SUM(T100.SellingShipQty) FROM InvcDtl_" + Parameters!TableGuid.Value + " T100 WHERE T2.Company = T100.Company AND T2.InvoiceNum = T100.InvoiceNum) AS InvcDtl_SellingShipQty