You're gallery's XML file looks fine (no errors).
The information in the FAQ (https://www.juicebox.net/support/faq/#local) is still relevant and should work OK.
It is important to note that you can only preview galleries locally (from your computer's hard drive) in Firefox or Safari and only after changing the setting noted in the FAQ.
It is not possible to preview galleries locally in any other browser.
Please let me know what browser (and version number) you are using and please confirm that you have changed the relevant setting in your browser's configuration options.
This only applies to previewing galleries locally. There is no issue once the galleries have been uploaded to a web server where they can be viewed in any modern browser without any settings needing to be changed.
If you have uploaded a gallery to a web server and still see the 'Config file not found.' error message, then please post a link to the dysfunctional gallery so that I can see the problem for myself.
Once I can see the problem live on your web server, I should be able to determine the exact cause of the problem and propose a solution.
Thank you.
(The easiest way to upload and view a gallery is to upload the entire gallery folder to your web server (with an FTP program such as Filezilla) and then open the 'index.html' page (inside the gallery folder) in a browser.)