Loosing pefix of the messages when append to textbox

I developed program that has 2 listening sockets and 2 text boxes for incoming messages and outgoing messages. Program receives messages from sockets connected to first listening socket and sends them to all sockets connected to second listening socket. When a message is appended to a textbox to the message is added a prefix. For some of the messages displayed the prefix disappears. Also some messages are not sent out. I use method send with while loop to assure that the messages are sent. There are not exceptions. Please Help. Below are the codes. public void AppendMesToOutgTB(int indexOfSocket, eServerClient TypeOfSocket, string Message) { string Clt = "Clt"; string Srv = "Srv"; string Sep = ":"+Environment.NewLine; Socket workerSocket; StringBuilder sb = new StringBuilder(1000); //string Addr;// = ((IPEndPoint)workerSocket.RemoteEndPoint).Address.ToString(); switch (TypeOfSocket) { case eServerClient.eClient: //if (!m_workerClientSocketList.IsLoginOk(indexOfSocket)) //break; workerSocket = (Socket)m_workerClientSocketList[indexOfSocket]; //Addr = ((IPEndPoint)workerSocket.RemoteEndPoint).Address.ToString(); sb.Append(Clt);// + Addr + Sep + Message + Environment.NewLine); sb.Append(((IPEndPoint)workerSocket.RemoteEndPoint).Address.ToString());// + Sep + Message + Environment.NewLine); sb.Append(Sep);// + Message + Environment.NewLine); sb.Append(Message);// + Environment.NewLine); sb.Append(Environment.NewLine); tbOutgoingMes.AppendText(sb.ToString()); break; case eServerClient.eServer: workerSocket = (Socket)m_workerServerSocketList[indexOfSocket]; sb.Append(Srv);// + Addr + Sep + Message + Environment.NewLine); sb.Append(((IPEndPoint)workerSocket.RemoteEndPoint).Address.ToString());// + Sep + Message + Environment.NewLine); sb.Append(Sep);// + Message + Environment.NewLine); sb.Append(Message);// + Environment.NewLine); sb.Append(Environment.NewLine); tbOutgoingMes.AppendText(sb.ToString()); break; } } public void AppendMesToIncTB(Socket workerSocket, string szData) { string Clt = "Clt"; string Srv = "Srv"; string Sep = ":"+Environment.NewLine; StringBuilder sb = new StringBuilder(1000); if (m_workerClientSocketList.Contains(workerSocket)) { sb.Append(Clt);// + Addr + Sep + Message + Environment.NewLine); sb.Append(((IPEndPoint)workerSocket.RemoteEndPoint).Address.ToString());// + Sep + Message + Environment.NewLine); sb.Append(Sep);// + Message + Environment.NewLine); sb.Append(szData);// + Environment.NewLine); sb.Append(Environment.NewLine); tbIncomingMes.AppendText(sb.ToString()); } else if (m_workerServerSocketList.Contains(workerSocket)) { sb.Append(Srv);// + Addr + Sep + Message + Environment.NewLine); sb.Append(((IPEndPoint)workerSocket.RemoteEndPoint).Address.ToString());// + Sep + Message + Environment.NewLine); sb.Append(Sep);// + Message + Environment.NewLine); sb.Append(szData);// + Environment.NewLine); sb.Append(Environment.NewLine); tbIncomingMes.AppendText(sb.ToString()); } }