Erro

trocarSenha.php
<?
  require_once 'AuthMe.class.php';
  $am = new AuthMe("sql-7.verygames.net", "db455348", "8wj9brh6x", "db455348", "authme");

  $username = $_POST['username'];
  $newpass  = $_POST['password'];

  $change = $am->changePassword($username, $newpass);

  if($change){
    echo
    '
    <script>alert("Senha alterado com sucesso!"); history.back();</script>
    ';
  }else{
    echo
    '
    <script>alert("Erro ao trocar senha!"); history.back();</script>
    ';
  }
?>

AuthMe.class.php
<?php

class AuthMe {

    const MD5 = "md5";

    private $conection;

    private $authme_table;

    private $algorithm;

    public function __construct($db_host, $db_user, $db_pass, $db_name, $authme_table) {
        $this->authme_table = $authme_table;
        $this->algorithm = MD5;
        @$this->conection = mysqli_connect($db_host, $db_user, $db_pass) or die(mysqli_connect_error());
        @mysqli_select_db($this->conection, $db_name) or die(mysqli_error($this->conection));
    }

    public function __destruct() {
        if (is_object($this->conection)) {
            $this->conection->close();
            unset($this->algorithm);
            unset($this->authme_table);
        }
    }

    public function changePassword($username, $newpass) {
        if (!self::isUsernameRegistered($username)) {
            return false;
        }

        $username = addslashes($username);
        $newpass = addslashes(self::AMHash($newpass));

        return mysqli_query($this->conection, "UPDATE {$this->authme_table} SET password='$newpass' WHERE username='$username'");
    }

    public function isIpRegistered($ip) {
        $ip = addslashes($ip);
        $query = mysqli_query($this->conection, "SELECT ip FROM {$this->authme_table} WHERE ip='{$ip}'");
        return mysqli_num_rows($query) >= 1;
    }


    public function isUsernameRegistered($user) {
        $user = addslashes($user);
        $query = mysqli_query($this->conection, "SELECT username FROM {$this->authme_table} WHERE username='{$user}'");
        return mysqli_num_rows($query) >= 1;
    }

    private function compare($pass, $hash_pass) {
        switch ($this->algorithm) {

            case "sha256":
                $shainfo = explode("$", $hash_pass);
                $pass = hash("sha256", $pass).$shainfo[2];
                return strcasecmp($shainfo[3], hash('sha256', $pass)) == 0;

            case "sha1":
                return strcasecmp($hash_pass, hash('sha1', $pass)) == 0;

            case "md5":
                return strcasecmp($hash_pass, hash('md5', $pass)) == 0;

            case "whirlpool":
                return strcasecmp($hash_pass, hash('whirlpool', $pass)) == 0;

            case "md5vb":
                $shainfo = explode("$", $hash_pass);
                $pass = hash("md5", $pass).$shainfo[2];
                return strcasecmp($shainfo[3], hash('md5', $pass)) == 0;

            case "plaintext":
                return $hash_pass == $pass;

            default:
                return false;
        }
    }

    private function AMHash($pass) {
        switch ($this->algorithm) {

            case "sha256":
                $salt = self::createSalt();
                return "\$SHA\$".$salt."\$".hash("sha256", hash('sha256', $pass).$salt);

            case "sha1":
                return hash("sha1", $pass);

            case "md5":
                return hash("sha1", $pass);

            case "whirlpool":
                return hash("sha1", $pass);

            case "md5vb":
                $salt = self::createSalt();
                return "\$MD5vb\$".$salt."\$".hash("md5", hash('md5', $pass).$salt);

            case "plaintext":
                return $pass;

            default:
                return false;
        }
    }

    private function createSalt() {
        $salt = "";
        for ($i = 0; $i < 20; $i++) {
            $salt .= rand(0, 9);
        }
        return substr(hash("sha1", $salt), 0, 16);
    }
}