mysqli_num_rows PHP помогите решить

LOG ERORR :____________________________________________________
mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in /home/freebit2/public_html/guest/account.php on line 11
_______________________________________________________________

<?

if ($_POST['register_f']) {

valid_captcha();
valid_name();
valid_wallet();

db();

if (mysqli_num_rows(mysqli_query($db, "SELECT `id` FROM `users` WHERE `wallet` = '$_POST[wallet]'")))
message('Этот кошелек уже зарегистрирован');

if ($_SESSION['ref'])
$ref = $_SESSION['ref'];
else
$ref = 0;

mysqli_query($db, "INSERT INTO `users` VALUES('', $ref, '$_POST[name]', '$_POST[wallet]', 0, '$_SERVER[REMOTE_ADDR]', 0, 0, 0)");

message('Регистрация завершена');
}

else if ($_POST['login_f']) {

valid_captcha();
valid_wallet();
db();

$query = mysqli_query($db, "SELECT * FROM `users` WHERE `wallet` = '$_POST[wallet]'");

if (!mysqli_num_rows($query))
message('Аккаунт не найден');

$row = mysqli_fetch_assoc($query);

if ($row['protect'] == 1 and $row['ip'] != $_SERVER['REMOTE_ADDR'])
message('Доступ с этого IP запрещен');
else if ($row['ban'] == 1)
message('Аккаунт заблокирован');

foreach ($row as $key => $val)
$_SESSION[$key] = $val;

$refq = mysqli_query($db, "SELECT `name`, `balance` FROM `users` WHERE `ref` = $_SESSION[id] ORDER BY `id` DESC LIMIT 10");

if (mysqli_num_rows($refq)) {
while ($refr = mysqli_fetch_assoc($refq))
$_SESSION['reflist'][] = array($refr['name'], $refr['balance']);
}

go('profile');

}

else if ($_POST['bonus_f'])
message('Для получения бонуса пройдите регистрацию');

?>