public void createErrorWindow(Window owner) {
            WindowCreator creator = new WindowCreator(owner);
            JDialog dialog = creator.createNewJDialog("Error!", 470, 140);

            JPanel mainPanel = new JPanel();
            Border padding = BorderFactory.createEmptyBorder(20, 20, 20, 20);

            mainPanel.setBorder(padding);
            mainPanel.setLayout(new GridLayout(2, 1, 20, 20));

            JPanel topPanel = new JPanel();            
            JLabel errorMessage = new JLabel("Number of simulations has to be a positive integer.");
            topPanel.add(errorMessage);
            mainPanel.add(topPanel);
            
            JPanel bottomPanel = new JPanel();
            bottomPanel.setLayout(new GridLayout(1,3,20,20));
            
            JButton okButton = new JButton("OK");
            okButton.addActionListener(new CloseWindow(dialog));
            bottomPanel.add(new JLabel(""));
            bottomPanel.add(okButton);
            bottomPanel.add(new JLabel(""));            
            
            mainPanel.add(bottomPanel);
            
            dialog.setContentPane(mainPanel);           
    }