thank you

same problem after applying file headerwith name length and data

try
                {
                    byte[] clientData = new byte[1024 * 5000];
                    int receivedBytesLen = s.Receive(clientData);
                    byte[] b = clientData;
                    int fileNameLen = BitConverter.ToInt32(clientData, 0);
                    
                    fileName = Encoding.ASCII.GetString(clientData, 4, fileNameLen);
                    byte[] l = Encoding.ASCII.GetBytes(fileName);
                    Console.WriteLine("Client:{0} connected & File {1} started received.", s.RemoteEndPoint, fileName);

                    string temp = System.Text.Encoding.UTF8.GetString(b, 3 + fileNameLen, receivedBytesLen); // the line causing the error i think.
                    fileBytes = System.Text.Encoding.UTF8.GetBytes(temp);
                    Console.WriteLine("rec file");
                    
                }
                catch (Exception exx)
                {
                    Console.WriteLine(exx.ToString());
                    Console.Read();
                }

i understand the char problem. can u state the class to access the header or create one for the block?

Thanks i thought it will add the label again not over write it

Alf shokr ya basha. I tried this and it works and the form doesn't turn to not responding but it still doesn't show the MessageBox.Show(msg);
any ideas?