Sort results by timestamp not working

The docu says on https://github.com/alphapapa/org-rifle#tips

> **Sort results by timestamp** or buffer-order (the default) by calling commands with a universal prefix (C-u)

So I hit `C-u`, then `C-c q`, but I get an error message:

`helm-org-rifle-directories: No org files found in directories: ~/Dropbox/org`

But my org-agenda-files are in that folder, it's full of org files.