Error using codeigniter, grocerycrud and image_moo - codeigniter

Question

I have a question using codeigniter, grocerycrud and image_moo. The code is shown below. On a production server using xampp it works fine, but when uploading that same code to a server to publish it under linux gives error. He uploads the image correctly but when he tries to process the call to image_moo he returns a javascript error. I've tried to see by all means where the error is but no solution so far. Someone who gave you something similar could tell me how to solve it?
Thank you
public function index()
{
$crud = new grocery_CRUD();
$this->load->config ( 'grocery_crud' );
$this->config->set_item ( 'grocery_crud_file_upload_allow_file_types', 'gif|jpeg|jpg|png' );
$crud->set_theme ( 'datatables' );
$crud->set_table ( 'portafolio' );
$crud->set_subject ( 'imagen de portafolio' );
$crud->columns ( 'imagen', 'descripcion_es', 'descripcion_en', 'activa' );
$crud->required_fields ( 'activa', 'descripcion_es', 'descripcion_en', 'imagen' );
$crud->set_field_upload ( 'imagen', 'uploads/portfolio' );
$crud->display_as ( 'descripcion_es', 'Descripción ES' );
$crud->display_as ( 'descripcion_en', 'Descripción EN' );
//voy a reducir el tamano de la imagen siempre
$crud->callback_after_upload ( array ( $this, 'reducir_350' ) );
$output = $crud->render();
$data [ 'grid'] = $output->output;
$data [ 'css_files' ] = $output->css_files;
$data [ 'js_files' ] = $output->js_files;
$data ['titulo_pagina'] = 'Imágenes de portafolio';
$data ['menu_principal'] = $this->load->view ( 'back/view_menu', '', true );
$this->load->view ( 'back/view_base', $data );
}
function reducir_350 ( $uploader_response, $field_info, $files_to_upload )
{
$this->load->library ( 'image_moo' );
//Is only one file uploaded so it ok to use it with $uploader_response[0].
$file_uploaded = DIR_SITIO . $field_info->upload_path . '/' . $uploader_response[0]->name;
$file_savedto = DIR_SITIO . $field_info->upload_path . '/p-' . $uploader_response[0]->name;
$this->image_moo->load ( $file_uploaded )->resize_crop ( 350,250 )->save ( $file_savedto, true );
return true;
}