php / sql登录脚本故障排除

So, when I run this login script, I get the following error:

PHP Warning: mysql_real_escape_string() [function.mysql-real-escape-string]: A link to the server could not be established in (...) on line 116.

I'm calling the database at the top of the script, and not getting any errors from PEAR... print_r($db) returns an object...

code follows:

<?php

function &db_connect() { 
  require_once 'DB.php'; 
  PEAR::setErrorHandling(PEAR_ERROR_DIE); 
  $db_host = 'internal-db.xxxxx.gridserver.com'; 
  $db_user = 'xxxxx'; 
  $db_pass = 'xxxx'; 
  $db_name = 'xxxxx_wedding2'; 
  $dsn = "mysqli://$db_user:$db_pass@$db_host/$db_name"; 
  $db = DB::connect($dsn); 
  $db->setFetchMode(DB_FETCHMODE_OBJECT); 
  return $db; 
}
$db = &db_connect();
if (DB::isError ($db))
     die ("Cannot connect: " . $db->getMessage () . "
"); 

if (!isset($_SESSION['uid'])) {
  session_defaults();
}

function session_defaults() { 
  $_SESSION['logged'] = false; 
  $_SESSION['uid'] = 0; 
  $_SESSION['username'] = ''; 
  $_SESSION['cookie'] = 0; 
  $_SESSION['remember'] = false; 
}

class User {
  var $db = null; //PEAR::DB pointer
  var $failed = false; //failed login
  var $date;  //current date
  var $id = 0; //current users id

  function User(&$db) {   //is this the constructor?
    $this->db = $db;
    $this->date = $GLOBALS['date'];
    $this->role = $_SESSION['role'];
    if ($_SESSION['logged']) {
      $this->_check_Session();
    } elseif (!isset($_COOKIE['myLogin'])) {
      $this->_checkRemembered($_COOKIE['myLogin']);
    }

  }

   function _checkLogin($username, $password, $remember) {
    $username = $this->db->quote($username);  //uses PEAR::DB->quote method to sanitize input
    $password = $this->db->quote(md5($password)); // "  "
    $sql = "SELECT * FROM guest WHERE (username = $username) AND (password = $password)";
    $result = $this->db->getRow($sql);
    if (is_object($result)) {
      $this->_setSession($result, $remember);
      return true;
    } else {
      $this->failed = true;
      $this->_logout();
      print "Sorry, you have entered an invalid username or password!";
      return false;
    }
  }

  function _checkRemembered($cookie) {
    list($username, $cookie) = unserialize($cookie);
    if (!$username or !$cookie) return;
    $username = $this->db->quote($username);
    $cookie = $this->db->quote($cookie);
    $sql = "SELECT * FROM member WHERE (username = $username) AND (cookie = $cookie)";
    $result = $this->db->getRow($sql);
    if (is_object($result)) {
      $this->_setSession($result, true);    
    }  
  }

  function _setSession(&$values, $remember, $init = true) {
    $this->id = $values->id;
    $_SESSION['uid'] = $this->id;
    $_SESSION['username'] = htmlspecialchars($values->username);
    $_SESSION['cookie'] = $values->cookie;
    $_SESSION['logged'] = true;
    $_SESSION['role'] = $values->role;
    if ($remember) {
      $this->updateCookie($values->cookie, true);
    }
   /* if ($init) {
    $session = $this->db->quote($_SERVER['REMOTE_ADDR']);
    $sql = "UPDATE guest SET session = $session, ip = $ip WHERE id = $this->id";
    $this->db->query($sql);
    }*/
  }


  function updateCookie($cookie, $save) {
    $_SESSION['cookie'] = $cookie;
    if ($save) {
      $cookie = serialize(array($_SESSION['username'], $cookie));
      set_cookie;}
    }
  }

  function _logout() {
    session_defaults();
  }

  $date = time();
  $user = new User($db);
  $myusername = mysql_real_escape_string(stripslashes($_POST['myusername']));
  $mypassword = mysql_real_escape_string(stripslashes($_POST['mypassword'])); 
  $status  = $user->_checkLogin;
  print_r($status);

Any thoughts what I'm missing here? Is there a better way to troubleshoot my db connection?

Thanks in advance.