Error on System.exit(o)

 I get Error on System.exit(0).
 Please help.

 Regards Satish Kumar

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//import packages

import org.apache.log4j.*;
import com.jgoodies.plaf.plastic.PlasticXPLookAndFeel;
import com.jgoodies.plaf.plastic.theme.*;
import org.swixml.SwingEngine;
import javax.swing.*;
import java.awt.event.ActionEvent;

/*  Class Begins here*/
public class MessageDisplay
{

	private SwingEngine seMD;

	public JFrame fraTitle;
	public JLabel lblMessage;
	public JTextArea taMessage;
	public JTextArea taMsgTitle;
	public JTextArea taMsgHeader;

	/*	Constructor	*/
	public MessageDisplay(String title, String title_alt, String strMsg, String
strTxtArea) throws Exception
	{
		//	Look and Feel
		UIManager.setLookAndFeel(new PlasticXPLookAndFeel());
		PlasticXPLookAndFeel.setMyCurrentTheme(new ExperienceBlue());
		fraTitle.setDefaultLookAndFeelDecorated(true);

		//  Initialize SwingEngine
		seMD= new SwingEngine( this );
		seMD.render( "ps_lmi/xml/MessageDisplay.xml" );

		fraTitle.setTitle(seMD.getLocalizer().getString(title) );
		taMsgTitle.setText(seMD.getLocalizer().getString(title_alt) );
		taMsgHeader.setText(seMD.getLocalizer().getString(strMsg));
		taMessage.setText(seMD.getLocalizer().getString(strTxtArea));

		seMD.getRootComponent().setVisible( true );

		/*fraTitle.setTitle("License Manager:"+title);
		lblMessage.setText(strMsg);
		taMessage.setText(strTxtArea);*/
	}

	/* Description: This is invoked when OK is pressed	*/
	public AbstractAction actOK = new AbstractAction()
	{
		public void actionPerformed( ActionEvent e )
		{
			try
			{
				seMD.getRootComponent().setVisible( false );
				System.exit(1);
			}
			catch(Exception ex)
			{
				ex.printStackTrace();
			}
		}
	};