Cant write to a RandomAccessFile?

When I click loginbutton in the applet many errors are occuring and nothing is written to the file "Customer.txt"
The code is as follows...

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.io.*;
//<applet code=Login.class Width=400 Height=400>
//</applet>

public class Login extends JApplet implements ActionListener
{

      JTextField textcustname;
      JPasswordField textpassword;
      JLabel labelcustname;
      JLabel labelpassword;
      JButton loginbutton;
      public void init()
      {
            createApplet();
      }
      public void createApplet()
      {
            Container content;
            content=getContentPane();
            content.setLayout(new FlowLayout());
            labelcustname=new JLabel("Customer Login Name:");
            textcustname=new JTextField(10);
            labelpassword=new JLabel("Password:");
            textpassword=new JPasswordField(10);
            loginbutton=new JButton("Login");
            content.add(labelcustname);
            content.add(textcustname);
            content.add(labelpassword);
            content.add(textpassword);
            content.add(loginbutton);
            loginbutton.addActionListener(this);
      }
      public void actionPerformed(ActionEvent evt)
      {
            Object obj=evt.getSource();
            if(obj==loginbutton)
            {
                  String entry=textcustname.getText() +":"+new String(textpassword.getPassword());
                  try
                  {
                        RandomAccessFile logfile=new RandomAccessFile("D:\\java\\bin\\Customer.txt","rw");
                        logfile.seek(logfile.length());
                        logfile.writeBytes(entry);

                  }

                  catch(IOException e)
                  {
                        showStatus("Cannot write on to the log file"+e);
                  }
            }
      }
}

I even set the Policytool such that "Customer.txt" file has both read and write privileges.So any suggestions please? Thanks.