C# server socket error

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C#

Hello!

private void startsrv_Click(object sender, EventArgs e)
        {
            server.Start();
            Thread checkforip = new Thread(new ThreadStart(CheckForIPs));
            checkforip.Start();
            MessageBox.Show("Server nu1 started");
        }

        private void onlylistentobtn_Click(object sender, EventArgs e)
        {
            
            server2 = new TcpListener(IPAddress.Parse(onlytotxtbox.Text), 9998);
            server2.Start();
            TcpClient conn2 = server2.AcceptTcpClient();
            StreamWriter sw = new StreamWriter(conn2.GetStream());
            sw.WriteLine("1");
            sw.Flush();
            MessageBox.Show("Server nu2 started");
        }

Now when I debug it it stops at server2.Start(), exception: SocketException:The requested address is not valid in its context

What I can't understand is that the server.Start() starts server1, and I don't know why the second one doesn't.

Any ideas?