[java] Double Buffer

Sorry for such an elementary question. I'm attempting to code an aquarium "game" that is more like a hands-off simulation. I'm running into a problem with double buffering. When I try to createImage for the double buffer it returns a null. Hence when I try to get the Graphics context for the double buffer it throws a NullPointerException. I've looked hither and yon for the answer, googled, yahooed, searched archives and I can't seem to find exactly what I'm looking for. Here is the code. This is my panel class:

package aquarium;

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GraphicsEnvironment;
import java.awt.Image;
import java.awt.MediaTracker;
import java.awt.Rectangle;
import java.awt.Toolkit;
import javax.swing.JPanel;

/**
 *
 * @author Rob
 */
public class TankPanel extends JPanel {
    
    private MediaTracker mt;
    private Image backGround;
    private Image[] fishies;
    
    private Image buffBackGround;
    private Graphics buffGraphics;
    
    private Rectangle borders;
    
    /** Creates a new instance of TankPanel */
    public TankPanel() {
        
        super();
        this.setLayout(null);
        this.setDoubleBuffered(true);
        
        fishies = new Image[2];
        
        prepImage();
        prepBufferedImage();
        
        setPreferredSize(new Dimension(backGround.getWidth(this),
                                       backGround.getHeight(this)));
        
        borders = findBorders();
    }
    
    private void prepImage()
    {
        backGround = Toolkit.getDefaultToolkit().
                getImage("F:\\ProjFiles\\NBWorkspace\\Aquarium\\data\\bubbles.gif");
        fishies[0] = Toolkit.getDefaultToolkit().
                getImage("F:\\ProjFiles\\NBWorkspace\\Aquarium\\data\\fish1.gif");
        fishies[1] = Toolkit.getDefaultToolkit().
                getImage("F:\\ProjFiles\\NBWorkspace\\Aquarium\\data\\fish2.gif");
        
        mt = new MediaTracker(this);
        mt.addImage(backGround,0);
        mt.addImage(fishies[0],0);
        mt.addImage(fishies[1],0);
        
        try
        {
            mt.waitForAll();
        }
        catch (InterruptedException e){
            System.err.println("Error loading picture");
        }
        
        repaint();
        
    }
    
    private void prepBufferedImage()
    {
        buffBackGround = createImage(getSize().width,
                                          getSize().height);

        if(buffBackGround == null)
        {
            System.out.println("Buffered Image is null");
        }
        else
        {
            buffGraphics = buffBackGround.getGraphics();
        }
    }
    
    private Rectangle findBorders()
    {
        return new Rectangle(0 + getInsets().left, 
                             0 + getInsets().top,
                             getSize().width - (getInsets().left + getInsets().right),
                             getSize().height - (getInsets().top + getInsets().bottom));
    }
    
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        
        Dimension dim = this.getPreferredSize();
        
        g.drawImage(backGround,0,0,this);
        
    }
}

I can't seem to get a handle on this.