Why the opencv giving this error when multiple clients are connected in java?

edit

This is the Server side code which accepts multiple clients.

class Server extends Thread{

    @Override
    public void run(){
        UserArrayList=new ArrayList();
        try {
            Server=new ServerSocket(1013);
            while (true) {          

                ServerSocket=Server.accept();

                StreamVideo StartStreamVideo=new StreamVideo(ServerSocket);
                StartStreamVideo.start();
            }
        } catch (IOException ex) {
            Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
        }

    }
}

 class StreamVideo extends Thread{
     Socket NewSocket;
    public StreamVideo(Socket NewSocket) {
        this.NewSocket=NewSocket;
        WebCam=new VideoCapture(0); 
    }



     @Override
    public void run() {

       ObjectOutputStream SendMessage = null;
         try {
             SendMessage = new ObjectOutputStream(NewSocket.getOutputStream());
             while(true){
                 if(WebCam.grab()){
                     try {
                         Grabing=true;
                         WebCam.retrieve(Frame);
                         Imgcodecs.imencode(".jpg", Frame, mem); //This line gives the error when more than one client is connected 
                         Image Video=ImageIO.read(new ByteArrayInputStream(mem.toArray()));
                         BufferedImage SendVideo=(BufferedImage) Video;

                         Graphics DrawImage=jPanel1.getGraphics();
                         DrawImage.drawImage(SendVideo, 0, 0, getWidth(), getHeight()-100,0,0,SendVideo.getWidth(),SendVideo.getHeight(), null);
                         img=new ImageIcon(SendVideo);

                         SendMessage.writeObject(img);
                         SendMessage.reset();
                     } catch (IOException ex) {
                         Logger.getLogger(CamServer.class.getName()).log(Level.SEVERE, null, ex);
                     }
                 }
             }} catch (IOException ex) {
             Logger.getLogger(CamServer.class.getName()).log(Level.SEVERE, null, ex);
         } finally {
             try {
                 SendMessage.close();
             } catch (IOException ex) {
                 Logger.getLogger(CamServer.class.getName()).log(Level.SEVERE, null, ex);
             }
         }
    }
}

This is the client side code which get the Webcam stream form server.

  private void formWindowOpened(java.awt.event.WindowEvent evt) {                                  
  try {

        String Ip=GetIp();
        Socket ClientSocket=new Socket(Ip,1013);
        MsgOfServer=new ObjectInputStream(ClientSocket.getInputStream());

        GetStream getStream=new GetStream();
        getStream.start();


    }catch(IOException ex ){

    }
}                                 


private String GetIp(){
    return JOptionPane.showInputDialog(this, "Server IP Address");
}

class GetStream extends Thread{

    @Override
    public void run() {
        while (true) {        
            try {
                int x=0,y=0;
                ImageIcon imageIcon = (ImageIcon) MsgOfServer.readObject();                 
                Image image = imageIcon.getImage();
                image = image.getScaledInstance(jPanel1.getWidth(),jPanel1.getHeight(),Image.SCALE_SMOOTH);
                Graphics DrawImage=jPanel1.getGraphics();
                DrawImage.drawImage(image, 0, 0, jPanel1.getWidth(), jPanel1.getHeight(), null);
            } catch (IOException | ClassNotFoundException ex) {
                Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
            }

}

    }

}

and the error is

Exception in thread "Thread-6" Exception in thread "Thread-4" java.lang.Exception: unknown exception at org.opencv.videoio.VideoCapture.retrieve_1(Native Method) at org.opencv.videoio.VideoCapture.retrieve(VideoCapture.java:161) at CamServer$StreamVideo.run(CamServer.java:203) java.lang.Exception: unknown exception at org.opencv.videoio.VideoCapture.retrieve_1(Native Method) at org.opencv.videoio.VideoCapture.retrieve(VideoCapture.java:161) at CamServer$StreamVideo.run(CamServer.java:203) OpenCV Error: Unknown error code -10 (Raw image encoder error: Empty JPEG image (DNL not supported)) in cv::BaseImageEncoder::throwOnEror, file C:\builds\master_PackSlaveAddon-win64-vc12-static\opencv\modules\imgcodecs\src\grfmt_base.cpp, line 131 Exception in thread "Thread-7" CvException [org.opencv.core.CvException: cv::Exception: C:\builds\master_PackSlaveAddon-win64-vc12-static\opencv\modules\imgcodecs\src\grfmt_base.cpp:131: error: (-10) Raw image encoder error: Empty JPEG image (DNL not supported) in function cv::BaseImageEncoder::throwOnEror ] at org.opencv.imgcodecs.Imgcodecs.imencode_1(Native Method) at org.opencv.imgcodecs.Imgcodecs.imencode(Imgcodecs.java:166) at CamServer$StreamVideo.run(CamServer.java:204)

Please help me to solve this problem our give another way to do it.

Edited Code

    private void formWindowOpened(java.awt.event.WindowEvent evt) {                                  

    Server server=new ...