Error while append string to Textbox Text in VB.NET

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VB

TextBoxBase

Hai All,
I am developing one application in VB.net for Serialport reading from GSM Modem......While i read data from serialport that is append to string variable, after that i need to check weather that text is valid or not , if data is valid i append that text to TextBox.Text here I get one runtime error ie.,"Cross-thread operation not valid: Control 'TextBox1' accessed from a thread other than the thread it was created on." ------- InvalidOperation exception was unhandled....

Here I provide MY TOTAL CODE

Imports System.IO.Ports
Imports System.Windows.Forms.Form
Imports System
Public Class Main
    Dim WithEvents serialport As New SerialPort()
    Dim Rxd As String
    Public Rxd1 As String
    Private Sub Main_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        For Each sp As String In My.Computer.Ports.SerialPortNames
            ComboBox1.Items.Add(sp)
        Next
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            With serialport
                .PortName = ComboBox1.Text
                .BaudRate = "9600"
                .Parity = Parity.None
                .StopBits = StopBits.One
                .DataBits = 8
                .Handshake = Handshake.None
                .ReadBufferSize = 500
                .Open()
                AddHandler serialport.DataReceived, AddressOf serialport_DataReceived
                '.ReadBufferSize = 500
            End With

        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Me.Height = 743
        Me.Width = 1029
        Label8.Height = 30
        Label8.Width = 85
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        If serialport.IsOpen = True Then
            serialport.Write("$M1#")
        End If
    End Sub

    Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click

    End Sub

    Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
        serialport.WriteLine("$M1#")
    End Sub

    Private Sub serialport_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles serialport.DataReceived
        Dim sp As SerialPort = CType(sender, SerialPort)

        Dim menu_count As Integer
        Dim res As Integer
        Rxd = sp.ReadExisting
        menu_count = InStr(1, Rxd, "$M2", vbTextCompare)
        If menu_count > (500 - 189) Then
            sp.Write("$M1#")
        ElseIf menu_count Then
            menu_count = menu_count + 3
            For res = 0 To 5
                Rxd1 = Mid(Rxd, menu_count, 3)
                menu_count = menu_count + 3
                MsgBox(Rxd1)
                If res = 0 Then
                    Me.TextBox1.Text = Rxd1
                ElseIf res = 1 Then
                    TextBox2.Text = Rxd1
                ElseIf res = 2 Then
                    TextBox3.Text = Rxd1
                ElseIf res = 3 Then
                    TextBox4.Text = Rxd1
                ElseIf res = 4 Then
                    TextBox5.Text = Rxd1
                ElseIf res = 5 Then
                    TextBox6.Text = Rxd1
                End If
            Next
        End If
    End Sub

Me.TextBox1.Text = Rxd1

AT THIS POINT I GET ERROR

ANYBODY PLZZ HELP MEEEEE........