一段日期计算代码，在DataColChanged中，保存时出错，应该如何修改，请各位老师帮助指教，谢谢！！

 （内部表）

Dim mydate As Date = Forms("a").Controls("DateTimePicker1").Text
Dim y As Integer = mydate.Year
Dim m As Integer = mydate.Month
Dim Days As Integer = Date.DaysInMonth(y,m)
Dim yc As Date = New Date(y,m,1)  \'月初日期
Dim yd As Date = New Date(y,m,Days) \'月底日期
\'当月天数
Select Case e.DataCol.Name
    Case "编号"
        Dim dr As DataRow = e.DataRow
        If dr.IsNull("进厂日期") OrElse dr.IsNull("离厂日期") Then
            dr("当月天数") = 0
        Else
            If dr("进厂日期") <= #" & yc & "# And dr("离厂日期") > #" & yd & "# Then
                dr("当月天数") = #" & Days & "#
            Else
                dr("当月天数") = 0
            End If
        End If
End Select