Sessions

Ik krijg de volgende fout:

Warning: session_start(): Cannot send session cookie - headers already sent by (output started at /home/wo/public_html/index.php:6) in /home/wo/public_html/index.php on line 102

Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/wo/public_html/index.php:6) in /home/wo/public_html/index.php on line 102


En gebruik deze code:

<?
session_start();
if(session_is_registered('memberid')){
$query = mysql_query("SELECT * FROM vweb_members WHERE memberid = '$memberid'");

while($object = mysql_fetch_object($query)){
$gebruikersnaam = $object->gebruikersnaam;
$priveberichten = $object->pm;
}

$query = mysql_query("SELECT * FROM vweb_priveberichten WHERE naar = '$memberid'");
$result = mysql_num_rows($query);
?>
Ingelogd als: <? echo $gebruikersnaam ?><br>

&nbsp;&nbsp;- <a href="loguit.php">Log uit</a><br>
&nbsp;&nbsp;- <a href="profiel.php">Memberlijst</a><br>
&nbsp;&nbsp;- <a href="profiel.php?mid=<? echo $memberid ?>">Mijn profiel</a><br>
&nbsp;&nbsp;- <a href="wijzig.php">Wijzig gegevens</a><br>
<?
if($priveberichten){
?>
&nbsp;&nbsp;- <a href="priveberichten.php">Privé- berichten</a> ( <? echo $result ?> )

<?
}

}
else{
echo $a; //login scherm
}
?>

Wie kan me helpen?