codeigniter 3 file upload not working on iis

PHP Code:
public function post(){

          if (empty($this->input->post('post_text')) && empty($_FILES['image']['name'])) {
            redirect('posts');
          }

          $config['upload_path'] = './assets/images/postimages';
          $config['allowed_types'] = 'gif|jpg|png|jpeg';
          $config['max_size'] = '2048';

          $this->load->library('upload', $config);



          if (!empty($_FILES['image']['name'])) {

              if ($this->upload->do_upload('image')) {
                  $post_image = $_FILES['image']['name'];
                if ($this->Post_model->addPost($post_image)) {
                  array('upload_data' => $this->upload->data());
                  redirect('posts');
                }else{
                  $this->session->set_flashdata('post_errors', 'Sorry something went wrong, Please try again');
                  redirect('posts');
                }
            }else{
            //to diagnose i put else  here and put redirect function
              redirect('posts');
              //so i try to upload an image it always come to else, if i remove else and submit the form it just go to the url and stops
              like it go here http://localhost/friendmiiDemo/posts/post and stop
           }
            

          }else{
              if ($this->Post_model->addPost()) {
              redirect('posts');
            }else{
              $this->session->set_flashdata('post_errors', 'Sorry something went wrong, Please try again');
              redirect('posts');
            }
          }


}