problema header

[danirota]

echo "<table border=\"1\" bgcolor=\"#000000\">
            <tr><td><a href=\"forum.php\">Torna all'elenco dei viaggi</a></td></tr>
        ";

$id_forum = $_GET["id_forum"];
    $sql = "SELECT titolo_viaggio FROM viaggio WHERE id_viaggio=".$id_forum;
    //echo $sql;
    $res = mysql_query($sql);
    $row = mysql_fetch_array($res);
        $tit = $row["titolo_viaggio"];
        
        echo "<tr><td align=\"left\" valign=\"left\"><h2>".ucfirst($tit)."</h2></td>
                <td align=\"right\" valign=\"top\" width=\"178\"><a href=\"?action=SEL&com=YES&id_forum=".$id_forum."\">COMMENTA</a></td></tr>";
                


$com = $_GET["com"];                
if($com == "YES"){


            /*controllo login*/
            if($_SESSION["log"]==1){
                //echo "<h4>".$_SESSION["usr"]."</h4>";


    $id_forum = $_GET["id_forum"];

?>
<table border="1" cellpadding="0" cellspacing="0">
    <tr>
        <td>
            <table border="0" cellpadding="0" cellspacing="5">
                <tr>
                    <td>[img]./images/space.gif[/img]</td>
                </tr>
<form name="f_forum" method="post" action="">
        <tr>
            <td>[img]./images/space.gif[/img]</td>
            <td align="left">Nome</td>
            <td align="left"><? echo $_SESSION["usr"];  ?></td>
        </tr>
        <!--<tr>
            <td>[img]./images/space.gif[/img]</td>
            <td align="left">E-mail / Web page</td>
            <td align="left"><input type="text" name="contatto" value="<?php echo str_replace('"','&quot;',$_POST["contatto"]); ?>" class="input_forum"></td>
        </tr>-->
        <tr>
            <td>[img]./images/space.gif[/img]</td>
            <td  align="left">Scrivi il tuo messaggio</td>
            <td align="left"><textarea name="testo" class="input_forum" style="width:235px; height:120px; " ><?php echo $_POST["testo"];?></textarea></td>
        </tr>
        <tr>
            <td>[img]./images/space.gif[/img]</td>
            <td colspan="2" align="left">
                

                <input type="submit" value="Inserisci">
                <input type="hidden" name="db_action" value="INS">
                <input type="hidden" value="<?php echo $id_forum; ?>">
                
            </td>
        </tr>
</form>
                </table>
            </td>
        </tr>
    </table>
<?php
    }else{
        header('Location: /form.php');
    }
}