P8056-1 8Reles Card

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Hi, i am new on this page and i have problem with card P8056-1.
I read all instruction and PDF’s which describe how to communicate with card i am using.
I am working with vb.net 2008.

Can somebody help me with string and checksum below why i can not set the second relay ON for example?
Thank you for help awards.

My code looks like:
Public Class Form1

Function CheckSum(ByVal inStr As Char, ByVal relay As Char) As Integer
    Dim sum As Integer = (13 + 1 + Asc(inStr) + Asc(relay))
    Dim res As Integer = (255 - (sum Mod 256)) + 1
    Return res
End Function

Function SetSwitch(ByVal _On As Boolean, ByVal Relay As Char) As String
    Dim niz As String
    Dim inStr As Char
    If _On Then
        inStr = "S"
    Else
        inStr = "C"
    End If
    niz = "#13" + "1" + inStr + Relay + CType(CheckSum(inStr, Relay), String)
    Return niz
End Function


Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
    Dim _ports As New SerialPort

    With _ports
        .PortName = My.Settings.Com 'COM1
        .BaudRate = 2400
        .Parity = Parity.None
        .DataBits = 8
        .StopBits = StopBits.One
    End With

    _ports.Open()
    _ports.Write(SetSwitch(True, "2"))
    _ports.Close()

End Sub