Den vil ikke registrere sessionen!

<?
session_start();
session_register(\"username\");
include(\"connect.php\");
$sql = mysql_query(\"SELECT username,password FROM users WHERE username=\'$username\' and password=\'$password\'\");
print mysql_error();
if ($result = mysql_fetch_array($sql)) {
Header(\"Location: $HTTP_REFERER\");
}
else
{
session_unregister(\"username\");
Header(\"Location: index.php?action=fejl\");
}

?>