Codeigniter duplicate session issue

There is something wrong with your login code. You would need to post
some of your code here, so that we can see what your doing wrong.

LOGIN MODEL

Code:

public function login($email, $pass, $remember = FALSE) {

       // Remove cookies first
       $cookie = array(
           'name' => 'user',
           'value' => '',
           'expire' => time() - 3600,
           'path' => '/',
       );

       $this->CI->input->set_cookie($cookie);


       /*
        *
        * User Verification
        *
        * Removed or !ctype_alnum($pass) from the IF statement
        * It was causing issues with special characters in passwords
        * and returning FALSE even if the password matches.
        */
       if (!valid_email($email) OR strlen($pass) < 5 OR strlen($pass) > $this->config_vars['max']) {
           $this->error($this->CI->lang->line('aauth_error_login_failed'));
           return FALSE;
       }


       $query = null;
       $query = $this->CI->db->where('email', $email);
       $query = $this->CI->db->get($this->config_vars['users']);
       $row = $query->row();

       // only email found and login attempts exceeded
       if ($query->num_rows() > 0 && $this->config_vars['ddos_protection'] && !$this->update_login_attempts($row->email)) {

           $this->error($this->CI->lang->line('aauth_error_login_attempts_exceeded'));
           return FALSE;
       }

       //recaptcha login_attempts check
       $query = null;
       $query = $this->CI->db->where('email', $email);
       $query = $this->CI->db->get($this->config_vars['users']);
       $row = $query->row();
       if ($query->num_rows() > 0 && $this->config_vars['ddos_protection'] && $this->config_vars['recaptcha_active'] && $row->login_attempts >= $this->config_vars['recaptcha_login_attempts']) {
           $reCAPTCHA_cookie = array(
               'name' => 'reCAPTCHA',
               'value' => 'true',
               'expire' => time() + 7200,
               'path' => '/',
           );
           $this->CI->input->set_cookie($reCAPTCHA_cookie);
       }

       // if user is not verified
       $query = null;
       $query = $this->CI->db->where('email', $email);
       $query = $this->CI->db->where('banned', 1);
       $query = $this->CI->db->where('verification_code !=', '');
       $query = $this->CI->db->get($this->config_vars['users']);

       if ($query->num_rows() > 0) {
           $this->error($this->CI->lang->line('aauth_error_account_not_verified'));
           return FALSE;
       }

       // to find user id, create sessions and cookies
       $query = $this->CI->db->where('email', $email);
       $query = $this->CI->db->get($this->config_vars['users']);

       if ($query->num_rows() == 0) {
           $this->error($this->CI->lang->line('aauth_error_login_failed'));
           return FALSE;
       }

       $user_id = $query->row()->id;

       $query = null;
       $query = $this->CI->db->where('email', $email);

       // Database stores pasword hashed password
       $passwd = $this->hash_password($pass, $user_id);
       $query = $this->CI->db->where('pass', $passwd);
       //$query = $this->CI->db->where('pass', $this->hash_password($pass, $user_id));
       $query = $this->CI->db->where('banned', 0);

       $query = $this->CI->db->get($this->config_vars['users']);

       $row = $query->row();
       if ($this->CI->input->cookie('reCAPTCHA', TRUE) == 'true') {
           $reCaptcha = new ReCaptcha($this->config_vars['recaptcha_secret']);
           $resp = $reCaptcha->verifyResponse($this->CI->input->server("REMOTE_ADDR"), $this->CI->input->post("g-recaptcha-response"));

           if (!$resp->success) {
               $this->error($this->CI->lang->line('aauth_error_recaptcha_not_correct'));
               return FALSE;
           }
       }

       // if email and pass matches and not banned
       if ($query->num_rows() > 0) {

           // If email and pass matches
           // create session
           //get user_group
           $group = $this->get_user_groups($row->id);
           $mygroup = $group[0]->group_name;
           $data = array(
               'user_id' => $row->id,
               'firstname' => $row->firstname,
               'lastname' => $row->lastname,
               'phone' => $row->phone,
               'email' => $row->email,
               'centre_id' => $row->centre_id,
               'zone_id' => $row->zone_id,
               'mygroup' => $mygroup,
               'loggedin' => TRUE
           );

           $this->CI->session->set_userdata($data);

           // if remember selected
           if ($remember) {
               $expire = $this->config_vars['remember'];
               $today = date("Y-m-d");
               $remember_date = date("Y-m-d", strtotime($today . $expire));
               $random_string = random_string('alnum', 16);
               $this->update_remember($row->id, $random_string, $remember_date);

               $cookie = array(
                   'name' => 'user',
                   'value' => $row->id . "-" . $random_string,
                   'expire' => time() + 99 * 999 * 999,
                   'path' => '/',
               );

               $this->CI->input->set_cookie($cookie);
           }

           $reCAPTCHA_cookie = array(
               'name' => 'reCAPTCHA',
               'value' => 'false',
               'expire' => time() - 3600,
               'path' => '/',
           );
           $this->CI->input->set_cookie($reCAPTCHA_cookie);

           // update last login
           $this->update_last_login($row->id);
           $this->update_activity();
           $this->reset_login_attempts($row->id);

           return TRUE;
       }
       // if not matches
       else {

           $this->error($this->CI->lang->line('aauth_error_login_failed'));
           return FALSE;
       }
   }

LOGIN CONTROLLER

Code:

   function authentication() {
       $email = $this->input->post('email');
       $password = $this->input->post('password');
       $login = $this->aauth->login($email, $password);
       if ($login):

           redirect('dashboard/');
       else:
           $data['msg'] = $this->aauth->get_errors_array();
           $this->load->view('auth/login', $data);
       endif;
   }