Change your SQL to this and try:
SELECT tbl_idq_all.scode, Format([Date],"mm\/dd\/yyyy") AS poDate, tbl_idq_all.po_qty, DSum("po_qty","tbl_idq_all","[Date] < #" & [Date] & "# And scode='" & [scode] & "'")+Nz([po_qty],0) AS RunningTotal
FROM tbl_idq_all
ORDER BY tbl_idq_all.scode...