VB.NET 2010 Exception Comport read

Hello I read from comport whit followed code:

Public Class Form1
    Public Event DataReceived As SerialDataReceivedEventHandler

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        InitCOM1()
        InitCOM2()
        InitCOM3()

    End Sub


    ''' <summary>
    ''' Initering Comport 1
    ''' </summary>
    Public Sub InitCOM1()

        Dim COM1Comport As New SerialPort("COM1")
        COM1Comport.BaudRate = 9600
        COM1Comport.Parity = Parity.Even
        COM1Comport.StopBits = StopBits.One
        COM1Comport.DataBits = 8
        COM1Comport.Handshake = Handshake.None
        AddHandler COM1Comport.DataReceived, AddressOf DataReceivedHandler
        COM1Comport.Open()
        ' COM1Comport.Close()

    End Sub

    ''' <summary>
    ''' Initering Comport 2
    ''' </summary>
    Public Sub InitCOM2()

        Dim COM2Comport As New SerialPort("COM3")
        COM2Comport.BaudRate = 9600
        COM2Comport.Parity = Parity.Even
        COM2Comport.StopBits = StopBits.One
        COM2Comport.DataBits = 8
        COM2Comport.Handshake = Handshake.None
        AddHandler COM2Comport.DataReceived, AddressOf DataReceivedHandler
        COM2Comport.Open()
        ' COM2Comport.Close()

    End Sub

    ''' <summary>
    ''' Initering Comport 3
    ''' </summary>
    Public Sub InitCOM3()

        Dim COM3Comport As New SerialPort("COM4")
        COM3Comport.BaudRate = 9600
        COM3Comport.Parity = Parity.Even
        COM3Comport.StopBits = StopBits.One
        COM3Comport.DataBits = 8
        COM3Comport.Handshake = Handshake.None
        AddHandler COM3Comport.DataReceived, AddressOf DataReceivedHandler
        COM3Comport.Open()
        ' COM3Comport.Close()

    End Sub



    Public Sub DataReceivedHandler(ByVal sender As Object, ByVal e As SerialDataReceivedEventArgs)
        Dim sp As SerialPort = CType(sender, SerialPort)
        Dim indata As String = sp.ReadExisting()


        If sp.PortName = "COM3" Then
            ' MsgBox("COM3 " + indata)

            TextBox1.Text = ("COM3 " + indata)
        End If
        If sp.PortName = "COM4" Then

            TextBox1.Text = ("COM4 " + indata)
        End If

    End Sub

End Class

Select allOpen in new window

when I try to send the indata to a textbox on the form I get this ERROR

System.InvalidOperationException was unhandled
  Message=Cross-thread operation not valid: Control 'TextBox1' accessed from a thread other than the thread it was created on.
  Source=System.Windows.Forms
  StackTrace:
       at System.Windows.Forms.Control.get_Handle()
       at System.Windows.Forms.Control.set_WindowText(String value)
       at System.Windows.Forms.TextBoxBase.set_WindowText(String value)
       at System.Windows.Forms.Control.set_Text(String value)
       at System.Windows.Forms.TextBoxBase.set_Text(String value)
       at System.Windows.Forms.TextBox.set_Text(String value)
       at nyRs232.Form1.DataReceivedHandler(Object sender, SerialDataReceivedEventArgs e) in C:\Users\Automation West\Documents\Visual Studio 2010\Projects\nyRs232ff\nyRs232ff\Form1.vb:line 86
       at System.IO.Ports.SerialPort.CatchReceivedEvents(Object src, SerialDataReceivedEventArgs e)
       at System.IO.Ports.SerialStream.EventLoopRunner.CallReceiveEvents(Object state)
       at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state)
       at System.Threading.ExecutionContext.runTryCode(Object userData)
       at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
       at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
       at System.Threading.ThreadPoolWorkQueue.Dispatch()
       at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()
  InnerException:



However I can send it to a MsgBox(indata) thats works..

What do I do wrong??