Error message

• Notice: Undefined index: comment_node_liga_sitio_de_sitios_form in drupal_retrieve_form() (line 809 of includes/form.inc).
• Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'comment_node_liga_sitio_de_sitios_form' not found or invalid function name in drupal_retrieve_form() (line 844 of includes/form.inc).