测试了一下，你改了列名，对应代码没有修改。

If e.DataCol.Name = "销售出库日期" Then
    If e.DataRow.IsNull("销售出库日期") Then
        e.DataRow("出库单号") = Nothing
    Else
        Dim d As Date = e.DataRow("销售出库日期")
        Dim y As Integer = d.Year
        Dim m As Integer = d.Month
        Dim Days As Integer = Date.DaysInMonth(y,m)
        Dim fd As Date = New Date(y,m,1) \'获得该月的第一天
        Dim ld As Date = New Date(y,m,Days) \'获得该月的最后一天
        Dim bh As String = Format(d,"yyyyMM") \'生成编号的前6位,4位年,2位月.
        If e.DataRow("出库单号").StartsWith(bh) = False \'如果编号的前6位不符
            Dim max As String
            Dim idx As Integer
            max = e.DataTable.Compute("Max(出库单号)","销售出库日期>= #" & fd & "# And 销售出库日期<= #" & ld & "# And [_Identify] <> " & e.DataRow("_Identify")) \'取得该月的最大编号
            If max > "" Then \'如果存在最大编号
                idx = CInt(max.Substring(9,3)) + 1 \'获得最大编号的后三位顺序号,并加1
            Else
                idx = 1 \'否则顺序号等于1
            End If
            e.DataRow("出库单号") = "DN" & bh & "-" & Format(idx,"000")
        End If
    End If
End If