Big problem here, please help...

This is my entries-folder

_content
news
fields.yaml
page.md

My fields.yaml:

type: date
hide: true
_fieldset: newsdetail

This is my page.md

---
title: News
_fieldset: page
_template: newsliste
_default_folder_template: newsdetail
_default_folder_fieldset: newsdetail
_layout: home
---

This is my templates/newsdetail.html

<h1>Test</h1> <!-- just for render testing only -->

The news-page entries listing works perfectly, but the entries detail site doesn't work at all...
It says: «We can't find your theme files. Please check your settings.»

And here you can test it in real-life: The entries-listing: http://www.unserschiff.ch/test/news/
The detail-page: http://unserschiff.ch/test/news/golem