รันโปรแกรมแต่ติด Error Date-time รัน4หน้าก็เป็น4หน้าเลยคะ อันนี้ต้องแก้ไขยังไงคะ

 Dim strInsert As String

        Conn = New SqlConnection(conStr)

        If Conn.State = ConnectionState.Closed Then
            Conn.Open()
        End If
        strInsert = "insert into Billing(CustomerID, BillingID, BillingDate,Total)" & _
        "values ('" & CID.Text & "','" & TextBox2.Text & "','" & DateTimePicker1.Value & "'," & TextBox7.Text & ")"
        command = New SqlCommand(strInsert, Conn)
        command.ExecuteNonQuery()

        Dim DR As DataGridViewRow
        For Each DR In DataGridView2.Rows
            strInsert = "insert into BillingP(BillingID, Invoice, DateIV, Amount, Payment, Overdue )" & _
     "values ('" & TextBox2.Text & "','" & DR.Cells(0).Value & "','" & CDate(DR.Cells(1).Value) & "'," & DR.Cells(2).Value & ",'" & DR.Cells(3).Value & "'," & DR.Cells(4).Value & ")"
            command = New SqlCommand(strInsert, Conn)
            command.ExecuteNonQuery()
        Next



        MsgBox("บันทึกข้อมูลเรียบร้อยแล้ว")