mysql_fetch_object(): supplied argument is not a valid MySQL result resource

In dit script:

<?php
session_start();
ob_start();
include("data.php");

if (!empty($_POST)) {
$ip = $_SERVER['REMOTE_ADDR'];
$query = "SELECT * FROM members2 WHERE ip= '".$ip ."'";
$res = mysql_query($query) or die (mysql_error());
while($list = mysql_fetch_object($res)){
$poster = $list->naam;
$email = $list->email;

$categorie = $_POST[categorie];
$titel = $_POST[titel];
$bericht = $_POST[bericht];
$datum = date('d-m-Y H:i');
$sql = "
INSERT INTO serie1 (categorie, titel, poster, email, bericht,datum)
VALUES ('$categorie','$titel','$poster','$email','$bericht','$datum')
";
$resultaat = mysql_query($sql) or die (mysql_error());
header("Location:serie 1 overzicht.php");
exit;
}
}
else
{
echo '<center><form action=serie1.php method=post>
Categorie:<br /><br />
<select name=categorie><option value=serie1>Serie1</option>
<option value=serie2>Serie2</option>
<option value=serie3>Serie3</option></select><br /><br />
Titel:<br /><br />
<input type="text" maxlength="50" size="50" value="" name="titel"></input><br /><br />
Bericht: <br /><br />
<textarea rows="20" cols="100" value="" name="bericht"></textarea><br /><br />
<input type="submit" name="submit" value="Versturen">
</center>';
}
ob_end_flush();
?>

Krijg ik dus deze fout: Warning: mysql_fetch_object(): supplied argument is not a valid MySQL result resource in /usr/home/deb1230/domains/denhartoghkaas.nl/public_html/serie1.php on line 9

Weet iemand wat ik hieraan kan doen? Bij voorbaat dank!