BBcode qui génère un message vide

<?php 
function bbCode($t) 
{ 
$t=$data['message']; 
$t=str_replace("[b]", "<strong>", $t); 
$t=str_replace("[/b]", "</strong>", $t); 
return $t; 
} 

$base = mysql_connect ('sql.fai.fr', 'jean_dupont', 'monmotdepasse'); 
mysql_select_db ('nom_base', $base); 
$sql = 'SELECT id , auteur, email, date_signature, message FROM livre_or2 ORDER BY date_signature DESC'; 
$req = mysql_query($sql) or die('Erreur SQL !<br />'.$sql.'<br />'.mysql_error()); 
$nb_signature = mysql_num_rows($req); 
if ($nb_signature == 0) { 
 echo 'Aucun message enregistré.'; 
} 
else { 
 while ($data = mysql_fetch_array($req)) { 
  
                echo '<div class="content">' , '<img src="http://jean_dupont.fai.com/style/img/comm.png" title="' , ($data['id']); 
                echo '"><strong> '; 
                echo htmlentities(trim(stripslashes($data['auteur']))); 
  echo ' a dit : <br /><br /></strong>'; 
                echo bbCode($t); 
  echo '</div>'; 
 } 
} 
mysql_free_result ($req); 
mysql_close (); 
?>