Codeigniter set_userdata problem

[eluser]svkonur[/eluser]
hi guys im newbie in codeigniter. Im trying to create a session for user login but i cant do it. Session library auto loaded.
here is my codes i hope there is someone to help me asap. Regards.

Code:

if($this->form_validation->run()){
   $user_name = $this->input->post('user_name',TRUE);
   $user_pass = md5($this->input->post('user_pass',TRUE));
  
   try{
    $_control = $this->admin_model->check_user($user_name,$user_pass);
    if($_control != 0){
     //$ses_arr = array("user_name" => $_control[0]["user_name"]);
     try{
      if($this->session->set_userdata("user_name" , $_control[0]["user_name"])){
       redirect('admin');
      }else{
       throw new Exception('Oturum açma sorunu gerçekleşti.');
      }
     }
    
     catch(Exception $ses_excp){
      echo '<div class="alert alert-error"><button data-dismiss="alert" class="close" type="button" title="Kapat">×</button><center>'.$ses_excp->getMessage().'</center></div>';
     }
    }else{
     throw new Exception('Kullanıcı Bulunamadı!');
    }
   }
  
   catch(Exception $user_excp){
    echo '<div class="alert alert-error"><button data-dismiss="alert" class="close" type="button" title="Kapat">×</button><center>'.$user_excp->getMessage().'</center></div>';
   }
  }