Dropdownbox der lister ting fra MYSQL

Hej
Jeg har lavet en dropdownbox, der skal hente data ind fra databasen, det den skal hente ind har fået en værdi ($value) fra forrige side (hvor der var en ganske alm. html kodet dropdownbox). Mit problem er bare at der kommer en fejlmeddelelse der hedder:

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in ... line 16

Koden
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<?
include_once ("db_connect.php");

$query = "SELECT * FROM subsites WHERE subsitesid=$value";
    $db = new database('mysql');
    $result_subsites=$db->query($query,"rows");

//$result_mainsites = mysql_query("SELECT * FROM mainsites ORDER BY mainsitesname");

while ($row_mainsite = mysql_fetch_array($result_subsites, MYSQL_ASSOC)) {
  $print_subsite_list .= "<option value=\"" . $row_subsite["mainsitesid"] . "\">" . $row_subsite["subsitesname"] . "</option>\n";
}
/*If ($value=1)
{$listbox=;
}*/
?>
<html>
<head>
        <title>Title here!</title>
<form method=get action="ret3.php">
<select name="subsites" style="width:150">
<option value="0">Vælg side</option>
<?= $print_subsite_list ?>
</select>
</body>
</html>


Hvad er der galt?