session - cakephp issue - php

public function ajax_index(){

        $this->autoRender = false;

        if ($this->request->is('ajax')){

            Sanitize::clean($this -> request -> data['Participant']);

            $clean_data = array();
            $clean_data['vote'] = $this->Session->read('id');


            $this -> Participant -> set($clean_data);

            if ($this -> Participant -> save($clean_data)) {

                return true;
            }
            else{

                $errors = "";
                foreach($this->Participant->validationErrors as $key => $val){
                    foreach ($val as $index => $error_msg){
                        $errors  .= $error_msg . "<br />";
                    }
                }


                return $errors;

            }

        }

    }