Could not find the main class (with every jar)

Question

This isn't a developer question. I get the error Could not find the main class with every jar I try to open (for example the jar downloaded from https://gjar.dev.java.net/ gives the same problems - and I don't think there is something wrong with that JAR). It isn't a problem with the jar or MANIFEST because the same jar works fine on my laptop. So there is something wrong with my JRE installation, but what?
I tried to remove and reinstall the JRE 6 Update 18 but that didn't work. When I run the JAR with command line java -jar "file.jar" it works fine, but if I dubbelclick on it I get the error message (and it's irritating me).
I'm a bit desperate so I hope that someone here can help me ;)
Thanks in advanced

Answer 1

hai T.B.M ... Sorry to post here... I know that i posted my question in wrong thread..but i dont have another solution to contact with you.. I had seen your answers which are really excellent and helped to do my project..
Now i am having very less time to complete my project and i am very new to JMF.. I am not getting output in JMF video capture ..please check the code and guide me where i gone wrong.......please pardon me once again to post here.. Heres my code
import javax.media.*;
import java.awt.*;
import javax.swing.*;
import java.util.*;
import java.awt.event.*;
import javax.media.protocol.*;
import java.io.*;
import javax.media.control.StreamWriterControl;
public class webcam implements ActionListener,ControllerListener
boolean eomReached = false;
boolean realized = false;
JFrame f;
BorderLayout bd1;
CaptureDeviceInfo device;
MediaLocator m1;
Player player;
Component videoScreen;
JButton b1,b2;
Processor processor;
DataSource ds=null;
DataSink fileWriter=null;
JLabel status=new JLabel("");
public webcam()
try
JFrame f=new JFrame();
JPanel p =new JPanel();
JPanel p1=new JPanel();
device=CaptureDeviceManager.getDevice("vfw:Microsoft WDM Image Capture (Win32):0");
m1=device.getLocator();
System.out.println("1");
processor.configure();
processor = Manager.createProcessor(m1);
processor.setContentDescriptor(new
FileTypeDescriptor(FileTypeDescriptor.MSVIDEO));
ds=processor.getDataOutput();
player.addControllerListener(this);
MediaLocator dest = new MediaLocator("file://foo.avi");
fileWriter = Manager.createDataSink(ds, dest);
fileWriter.open();
ds.connect();
ds.start();
player=Manager.createPlayer(m1);
player.addControllerListener(this);
blockingRealize();
videoScreen=player.getVisualComponent();
b1=new JButton("START");
b2=new JButton("STOP");
bd1=new BorderLayout();
p.setLayout(bd1);
p1.add(b1);
p1.add(b2);
p.add("South",p1);
p.add("East",videoScreen);
f.getContentPane().add(p);
f.setVisible(true);
f.setSize(500,500);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
b1.addActionListener(this);
b2.addActionListener(this);
catch(Exception e){}
public void actionPerformed(ActionEvent e)
if(e.getSource()==b1)
try{
processor.start();
player.start();
fileWriter.start();
catch(Exception e1){}
if(e.getSource()==b2)
try{
player.stop();
processor.stop();
processor.close();
fileWriter.close();
catch(Exception e2){}
public static void main(String args[])
webcam obj=new webcam();
public synchronized void blockingRealize() {
player.realize();
while (!realized) {
try {
wait();
} catch (java.lang.InterruptedException e) {
status.setText("Interrupted while waiting on realize...exiting.");
System.exit(1);
public synchronized void controllerUpdate (ControllerEvent event) {
System.out.println("myPlayer generated "+event.toString());
if (event instanceof RealizeCompleteEvent) {
realized = true;
notify();
} else if (event instanceof EndOfMediaEvent) {
eomReached = true;
}