Imports System.Net
Imports System.Net.Sockets
Imports System.IO

Public Class mainForm

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

    Dim blah As backgroundServer

    initServer()

    blah = New backgroundServer
    blah.bgServerInstance.RunWorkerAsync()

    '        updateServerLabel("called from main")    <--works

End Sub


Public Sub updateServerLabel(ByVal strMessage As String)

    lblServerInfo.Text = strMessage

End Sub

End Class

Imports System.Net
Imports System.Net.Sockets
Imports System.IO

Module bgServer

Public strLocalIP As String
Public strHostName As String
Public intPortNumber As Int32

Public Sub initServer()
    strHostName = System.Net.Dns.GetHostName()
    strLocalIP = System.Net.Dns.GetHostEntry(strHostName).AddressList(0).ToString
    intPortNumber = 1052

    '        mainForm.updateServerLabel("called from init")     <--works
End Sub


Public Class backgroundServer

    Public WithEvents bgServerInstance As New System.ComponentModel.BackgroundWorker

    Private Sub bgServerInstance_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgServerInstance.DoWork

        Dim server As TcpListener = Nothing
        Dim client As TcpClient = Nothing
        Dim stream As NetworkStream = Nothing
        Dim port As Int32 = 8888
        Dim localAddr As IPAddress = IPAddress.Parse(strLocalIP)

        Dim data As String = Nothing
        Dim i As Int32
        Dim bytes(1024) As Byte
        Dim retMsg As Byte() = System.Text.Encoding.ASCII.GetBytes("Default Reply")

        mainForm.updateServerLabel("called from bg")   '<-- does not work

        server = New TcpListener(localAddr, port)
        server.Start()

        While (True)

            Try
                client = server.AcceptTcpClient()

                MsgBox("client accepted!")    '<--works

                client.Close()
            Catch ex As Exception
                MsgBox(ex.Message)
            End Try

        End While

    End Sub

End Class

End Module