Login Not work in host

[eluser]Hamed[/eluser]
Hello,
I have one login which work on local host but it doesn't work on web server:
This is my class for login:
<?php

if (!defined('BASEPATH'))
exit('No direct script access allowed');

/**
* @author Ali Ghasemzadeh
* @copyright 2012
* @website http://ghasemzadeh.ir
* @email [email protected]
*/


class User extends CI_Model
{
public $isLogin = false;
public function __construct()
{
parent::__construct();
date_default_timezone_set($this->config->item('default.time.zone'));
if ($this->session->userdata('uid')) {
$sid = $this->session->userdata('sid');
$now = time();
$query = $this->db->query("SELECT * FROM `online` WHERE sid = '$sid' AND expireTime > $now LIMIT 1");
if($query->num_rows() == 1) {
if($this->session->userdata('reminder') == 1) {
$ntime = time() + $this->config->item('expire.time.reminder') * 24 * 60 * 60;
} else {
$ntime = time() + $this->config->item('expire.time') * 60;
}
$nurl = $_SERVER['REQUEST_URI'];
$this->db->query("UPDATE `online` SET `lastClick` = '$nurl', `expireTime` = '$ntime' WHERE `sid` = '$sid';");
$this->isLogin = true;
} else {
$this->session->sess_destroy();
$this->isLogin = false;
}
} else {
$this->isLogin = false;
}
}

public function randomString($length)
{
$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$randomString = '';
for ($i = 0; $i < $length; $i++)
{
$randomString .= $characters[rand(0, strlen($characters) - 1)];
}
return $randomString;
}

public function login($username, $password, $reminder)
{
$query = $this->db->query("SELECT * FROM `user` WHERE username='$username' AND password='$password' AND isEmailAct='1' LIMIT 1");
if ($query->num_rows() == 1)
{
if($reminder == 1) {
$expireTime = time() + $this->config->item('expire.time.reminder') * 24 * 60 * 60;
} else {
$expireTime = time() + $this->config->item('expire.time') * 60;
}
$time = time();
$user = $query->row_array();
$uid = $user['uid'];
$curIP = $_SERVER['REMOTE_ADDR'];
$lastLoginTime = time();
$url = $_SERVER['REQUEST_URI'];
$lastIP = $user['curIP'];
$this->db->query("DELETE FROM `online` WHERE `uid` = $uid OR expireTime < $time");
$this->db->query("UPDATE `user` SET `curIP` = '$curIP', `lastIP` = '$lastIP', `lastLoginTime` = '$lastLoginTime' WHERE `user`.`uid` = '$uid';");
$this->db->query("INSERT INTO `online` (`sid`, `uid`, `username`, `IP`, `lastClick`, `expireTime`) VALUES (NULL, '$uid', '$username', '$curIP', '$url', '$expireTime');");
$user['sid'] = $this->db->insert_id();
$user['reminder'] = $reminder;
$this->session->set_userdata($user);
$this->isLogin = true;
return true;
} else
{
return false;
}
}
public function logout()
{
$uid = $this->session->userdata('uid');
$time = time();
$this->session->sess_destroy();
$this->db->query("DELETE FROM `online` WHERE `uid` = '$uid' OR expireTime < $time");
$this->isLogin = false;
return true;
}
public function register($username, $password, $email, $name, $family, $mobile, $sex, $address)
{
$mobileActCode = rand(1000, 9999);
$emailActCode = rand(1000, 9999);
$registerTime = time();
$registerIP = $_SERVER['REMOTE_ADDR'];
$this->db->query("INSERT INTO `user` (`uid`, `username`, `password`, `email`, `name`, `family`, `mobile`, `sex`, `address`, `newEmail`, `newMobile`, `emailActCode`, `mobileActCode`, `isEmailAct`, `isMobAct`, `isAdmin`, `registerTime`, `registerIP`, `curIP`, `lastIP`, `lastLoginTime`, `note`) VALUES (NULL, '$username', '$password', '$email', '$name', '$family', '$mobile', '$sex', '$address', '$email', '$mobile', '$emailActCode', '$mobileActCode', '0', '0', '0', '$registerTime', '$registerIP', '', '', '0', '');");
$uid = $this->db->insert_id();

//Sending Email
$this->load->library('email');
$this->email->from($this->config->item('email.sender.address'), $this->config->item('email.sender.name'));
$this->email->to($email);
$this->email->subject(lang('email.activation.subject'));
$link = base_url() . "auth/activeEmail/" . $uid . "/" . $emailActCode;
$this->email->message(lang('email.activation.message') . $link);
$this->email->send();

//Sending SMS

return true;
}

public function verfityEmail($email)
{
if(!filter_var($email, FILTER_VALIDATE_EMAIL))
{
return false;
}
$query = $this->db->query("SELECT * FROM `user` WHERE `email` = '$email' LIMIT 1");
if ($query->num_rows() == 1)
{
return false;
} else
{
return true;
}
}
public function resendEmailActivation($email) {
if(!filter_var($email, FILTER_VALIDATE_EMAIL))
{
return false;
}
$query = $this->db->query("SELECT * FROM `user` WHERE `email` = '$email' LIMIT 1");
if ($query->num_rows() == 1)
{
$user = $query->row();
$uid = $user->uid;
$emailActCode = $user->emailActCode;
$email = $user->email;
//Sending Email
$this->load->library('email');
$this->email->from($this->config->item('email.sender.address'), $this->config->item('email.sender.name'));
$this->email->to($email);

[eluser]Hamed[/eluser]
No one can help me?