Cannot access control on form from delegate routine

I am wiring a serial port handler class. The transmit and receive work and correct data is appearing in the ComBuffer in Serial_PortDataReceived event handler.

Next, I want to show the data in a label on the form so set up a delegate function "UpdateDisplay". In thi sroutine I convert the data byte array to string (mystr) and attempt to update the label1.text component on the form but it appears to not do anything. In the adjacent line I display mystr in a messagebox - this line works fine.

Any help much appreciated, I am new to delegates and threading (in fact new to OOP).

Code:

Imports System.IO.Ports

Public Class SerialConnection
    Dim port As SerialPort
    Private Delegate Sub UpdateFormDelegate()
    Private UpdateFormDelegate1 As UpdateFormDelegate
    Private comBuffer As Byte()

    Public Sub New(ByVal ComPort As String)
        Me.port = New SerialPort
        AddHandler port.DataReceived, AddressOf SerialPort_DataReceived
        With Me.port
            .PortName = ComPort
            .BaudRate = 115200
        End With
    End Sub

    Public Sub Open()
        If Not Me.port.IsOpen Then
            Try
                Me.port.Open()
                MessageBox.Show(Me.port.PortName & " Open")
            Catch ex As Exception
                MessageBox.Show(ex.Message & vbCrLf & "Select a port from the list")
            End Try
        End If
    End Sub

    Public Sub close()
        If Not Me.port.IsOpen Then Me.port.Close()
        MessageBox.Show("Port Closed")
    End Sub

    Public Sub Send(ByVal txdata As String)
        If Me.port.IsOpen Then
            If txdata <> "" Then
                Me.port.Write(txdata)
            Else
                MessageBox.Show("No Data to send")
            End If
        Else
            MessageBox.Show("Cannot send Message, Port not open")
        End If
    End Sub


    Private Sub SerialPort_DataReceived(ByVal sender As Object, ByVal e As SerialDataReceivedEventArgs)

        Dim n As Integer = Me.port.BytesToRead
        comBuffer = New Byte(n - 1) {}
        Me.port.Read(comBuffer, 0, n)

        UpdateFormDelegate1 = New UpdateFormDelegate(AddressOf UpdateDisplay)
        Me.UpdateFormDelegate1.Invoke()

    End Sub

    Private Sub UpdateDisplay()
        Dim mystr As String = System.Text.ASCIIEncoding.ASCII.GetString(comBuffer)

        If Form1.Label1.InvokeRequired Then
            Form1.Label1.Invoke(New MethodInvoker(AddressOf UpdateDisplay))
        Else
            MessageBox.Show(mystr)   ' this line shows received data ok
            Form1.Label1.Text = mystr  'this line is executed but appears to do nothing
        End If

    End Sub

End Class