My applet works in the appletviewer but not in the navigator

Question

My applet works in the appletviewer but not in the navigator
exceptions problem1 and problem2 are throwed
this is my code
import java.applet.*;
import java.net.*;
import java.io.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class ValiderHtml extends Applet implements ActionListener {
JButton send =new JButton("Connexion");
JScrollPane jscrollpane= new JScrollPane();
DefaultListModel lignes=new DefaultListModel();
JList lstURL = new JList(lignes);
BufferedReader reader = null;
String ligne;
URL url;
URLConnection conn;
   public void init(){   
   this.setSize(900,400);
   setLayout( new GridLayout(2,1));
   jscrollpane.setBounds(new Rectangle(19,53,160,73));
   jscrollpane.getViewport().add(lstURL,null);
   send.addActionListener(this);
        this.add(send);
   this.add(jscrollpane);
    public void actionPerformed(ActionEvent evt) {
         Send();
   public void Send(){
        try {
   url=new URL("http://www.developpez.com");
   conn = url.openConnection();
   reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
while ((ligne = reader.readLine()) != null) {
                 lignes.addElement(ligne);
    }//fin bloc try
   catch (Exception e) {
               lignes.addElement("probleme1");     
            finally{
               try{reader.close();}catch(Exception e){ lignes.addElement("probleme2");}
   }// fin Send
      public void paint(Graphics g) {
            super.paint(g);
}// fin Applet

Answer 1

As for tracking the source of your problem your applet sucks.
Try e.printStackTrace() on a cought exception and check the (full) trace.
url=new URL("http://www.developpez.com");
Unless yor applet is on www.developpez.com this will throw an exception in an unsigned
applet without special policies.
Signing applets:
http://forum.java.sun.com/thread.jsp?forum=63&thread=524815
second post and last post for the java class file
http://forum.java.sun.com/thread.jsp?forum=63&thread=409341
4th post explaining how to set up your own policy with your own keystore