paypal ipn working but stopping at 'thank you' page.

Question

I am using the code for controller(CODEIGNITER):

 function paypal_tran(){


  if (empty($_GET['action'])){ $_GET['action'] = 'process';}
   if($this->uri->segment ( 3 )){
    $action=$this->uri->segment ( 3 );
   }
  else{
    $action='process';
   } 

                              $ammount=39.99;
  $this->lenders_model->paypal_process($action,$this_script,$ammount);
  $this->load->view('view_paypal_tran');     






                    }

                    function ipn(){


                           if ($this->paypal_class->validate_ipn()) {



     $data = array(



      'fname'=> 'fname', /* insert the user id */

               'lname'=>'lname'


      );



     //$this->db->insert('ajax_test',$data);

         // For this example, we'll just email ourselves ALL the data.
         $subject = 'Instant Payment Notification - Recieved Payment';
         $to = '[email protected]';    //  your email
         $body =  "An instant payment notification was successfully recieved\n";
         $body .= "from ".$p->ipn_data['payer_email']." on ".date('m/d/Y');
         $body .= " at ".date('g:i A')."\n\nDetails:\n";

         foreach ($this->paypal_class->ipn_data as $key => $value) { $body .= "\n$key: $value"; }
         mail($to, $subject, $body);
      }









                    }


                    function success()
                    {

                             $this->load->view('paypal_succ_view');


                    }

AND this is my model:

    function paypal_process($action,$this_script,$ammount){


   switch ($action) {

   case 'process':      // Process and order...

      // There should be no output at this point.  To process the POST data,
      // the submit_paypal_post() function will output all the HTML tags which
      // contains a FORM which is submited instantaneously using the BODY onload
      // attribute.  In other words, don't echo or printf anything when you're
      // going to be calling the submit_paypal_post() function.

      // This is where you would have your form validation  and all that jazz.
      // You would take your POST vars and load them into the class like below,
      // only using the POST values instead of constant string expressions.

      // For example, after ensureing all the POST variables from your custom
      // order form are valid, you might have:
      //
      // $p->add_field('first_name', $_POST['first_name']);
      // $p->add_field('last_name', $_POST['last_name']);

      $this->paypal_class->add_field('business', '[email protected]');
      $this->paypal_class->add_field('return', $this_script.'/success');
      $this->paypal_class->add_field('cancel_return', $this_script.'/cancel');
      $this->paypal_class->add_field('notify_url', $this_script.'/ipn');
      $this->paypal_class->add_field('item_name', 'Lenders Account for one month');
      $this->paypal_class->add_field('amount', $ammount);

      $this->paypal_class->submit_paypal_post(); // submit the fields to paypal
      $this->paypal_class->dump_fields();      // for debugging, output a table of all the fields
      break;

PROBLEM IS IPN IS NOT WORKING. THE HIDDEN FIELD HAS VALUE FOR REDIRECT TO IPN, BUT NOT WORKING!!PLS HELP