Dim cn As Object, rs As Object, SumValue as Double
Set cn = CreateObject("ADODB.Connection")
Set rs = CreateObject("ADODB.Recordset")
cn.Open "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=путь\файл.mdb"
rs.Open "SELECT Sum(Value) AS SumValue FROM Table WHERE Value IS NOT NULL", cn, adOpenDynamic, adLockOptimistic
If Not (rs.EOF = True And rs.BOF = True) Then
     rs.MoveFirst
     If Not IsNull(rs.Fields("SumValue")) Then SumValue = CDbl(rs.Fields("SumValue")) Else SumValue =  0 
End If
On Error Resume Next
    rs.Close
On Error GoTo  0 
cn.Close
Set rs = Nothing
Set cn = Nothing