Premature end of script headers on form submission

Code:
function edit($id)

    {



        if($this->input->post('save')){



            $this->form_validation->set_rules(Category::NAME, Category::NAME, 'trim|required|alpha_dash');

            $this->form_validation->set_rules(Category::PERCENTAGE, Category::PERCENTAGE, 'trim|required|numeric');

            $this->form_validation->set_rules(Category::AVAILABLE, Category::AVAILABLE, 'trim|numeric');

            if($this->form_validation->run())

            {

                $category_array = array(

                    Category::CATID =>  $id,

                    Category::NAME  =>  $this->form_validation->set_value(Category::NAME),

                    Category::PERCENTAGE  =>  $this->form_validation->set_value(Category::PERCENTAGE),

                    Category::AVAILABLE  =>  $this->form_validation->set_value(Category::AVAILABLE) ? 1 : 0,

                );

                if($this->category->update($category_array))

                    $data['message'] = array('type' =>  'success', 'message' => 'ok message');

                else

                    $data['message'] = array('type' =>  'error', 'message' => 'not ok message'); 

            }else

                $data['message'] = array('type' =>  'error', 'message' => 'not ok message');



        }





        $data['category'] = $this->category->get_category($id);



        if(!$data['category'])

            redirect('categories');

        

        $output = $this->load->view('common/header', $data, true);

        $output .= $this->load->view('categories/edit', $data, true);

        $output .= $this->load->view('common/footer', $data, true);



        $this->output->set_output($output);

    }