A few issues here.
1) Your balance is wrong. Within the report details, you're just subtracting [debit]-[credit]. You need to create a running balance.
calculate-a-running-sum-cumulative-total[
^]
That's easy in Access 2007, just put a text box on the report and set it's 'RunningSum' property
2) In the 'Opening Balance' DSUM, replace with the following
=DSum("[debit]-(credit)","5 VoucherDetail","[vnum] = " & [Forms]![frmLedger]![Accid] & " AND [vDate] <= #" & [Forms]![frmLedger]![stdate] & "#")