Unable to add files on secure_notes_render_add_form

To reproduce:

Include a file field on your secure notes content type.
Create an invitation to make a secure note.
Follow the invitation link.
Upload a file (choose a file and press Upload).

You'll get an error:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'node_form' not found or invalid function name in drupal_retrieve_form() (line 841 of /var/www/zivtechnotes/code/includes/form.inc).

and the file upload widget is gone.

The attached patch fixes this by using form_load_include and drupal_build_form rather than module_load_include and the node_add function.