This question has already been answered:
Help, writes this error
Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in Z:\home\php\www\save_user.php on line 156.
Here is half the code:
$password = md5($password); $password = strrev($password); $password = $password."b3p6f"; include ("bd.php"); $result = mysql_query("SELECT id FROM users WHERE login='$login'",$db); $myrow = mysql_fetch_array($result); if (!empty($myrow['id'])) { exit ("Извините, введённый вами логин уже зарегистрирован. Введите другой логин."); }