RUNNING SUM IN FORM ACCESS 2007

[GEORGEKEAY]

Good morning,
I have problem to take the running sum in the form, i am working with Module, like that

Option Compare Database

Option Explicit
Public Function frmRunSum(frm As Form, pkName As String, sumName As String)
Dim rst As DAO.Recordset, fld As DAO.Field, subTotal

Set rst = frm.RecordsetClone
Set fld = rst(sumName)

'Set starting point.
rst.FindFirst "[" & pkName & "] = " & frm(pkName)

'Running Sum (subTotal) for each record group occurs here.
'After the starting point is set, we sum backwards to record 1.
If Not rst.BOF Then
Do Until rst.BOF
subTotal = subTotal + Nz(fld, 0)
rst.MovePrevious
Loop
Else
subTotal = 0
End If

frmRunSum = subTotal

Set fld = Nothing
Set rst = Nothing

End Function

Private Function SubSum()
'*************************************************************
'* pkName - Existing unique fieldname (usually primarykey) *
'* sumName - Name of the field to runsum *
'*************************************************************

If Trim(Me!pkName & "") <> "" Then 'Skip New Record!
SubSum = frmRunSum(Me, "pkName", "sumName")
End If

End Function




THEN I CALL IN THE FORM ON TEXTBOX SubSum() , like that Subsum([[DEPIT]) BUT IS NOT WORKING

THANKS FOR ANY ADVANCE