Sorry, let's try this:
INSERT INTO tblCombinedTopSellers ( ItemNo, Days, DailyAvg, NeedFor18Wks,
AtQty, VanQty, [Desc], Qty, [Order], Category )
SELECT TOP 25 tblCarts.ItemNo,
DateDiff("d",(Forms!frmTopSellers.StartDate),(Forms!frmTopSellers.EndDate))
AS Days,
[Qty]/DateDiff("d",(Forms!frmTopSellers.StartDate),(Forms!frmTopSellers.EndDate))
AS DailyAvg,
[Qty]/DateDiff("d",(Forms!frmTopSellers.StartDate),(Forms!frmTopSellers.EndDate))*126
AS NeedFor18Wks, tblAtlantaStock.AtQty, tblVancouverStock.VanQty,
tblItems.Desc, Sum(tblCarts.Qty) AS SumOfQty,
IIf([Qty]/DateDiff("d",(Forms!frmTopSellers.StartDate),(Forms!frmTopSellers.EndDate))*126-tblAtlantaStock!AtQty-tblVancouverStock!VanQty>0,(([Qty]/DateDiff("d",(Forms!frmTopSellers.StartDate),(Forms!frmTopSellers.EndDate))*126)-[AtQty]-[VanQty]),"
") AS [Order], "Clocks" AS Category
FROM ((tblItems INNER JOIN tblCarts ON tblItems.ItemNo = tblCarts.ItemNo)
INNER JOIN tblAtlantaStock ON tblItems.ItemNo = tblAtlantaStock.ItemNo)
INNER JOIN tblVancouverStock ON tblItems.ItemNo = tblVancouverStock.ItemNo
GROUP BY tblCarts.ItemNo,
DateDiff("d",(Forms!frmTopSellers.StartDate),(Forms!frmTopSellers.EndDate)),
[Qty]/DateDiff("d",(Forms!frmTopSellers.StartDate),(Forms!frmTopSellers.EndDate)),
[Qty]/DateDiff("d",(Forms!frmTopSellers.StartDate),(Forms!frmTopSellers.EndDate))*126,
tblAtlantaStock.AtQty, tblVancouverStock.VanQty, tblItems.Desc,
IIf([Qty]/DateDiff("d",(Forms!frmTopSellers.StartDate),(Forms!frmTopSellers.EndDate))*126-tblAtlantaStock!AtQty-tblVancouverStock!VanQty>0,(([Qty]/DateDiff("d",(Forms!frmTopSellers.StartDate),(Forms!frmTopSellers.EndDate))*126)-[AtQty]-[VanQty]),"
"), "Clocks", tblCarts.Date
HAVING (((tblCarts.ItemNo) Between "00001" And "09999" And
(tblCarts.ItemNo)<>"00000") AND ((tblCarts.Date) Between
[Forms]![frmTopSellers].[StartDate] And [Forms]![frmTopSellers].[EndDate]))
OR (((tblCarts.ItemNo) Between "40000" And "49999"))
ORDER BY Sum(tblCarts.Qty) DESC;