Is the Resource Groups container document in the Resource Group?
Are you using a plugin or a virtual host to route users to the right context?
Does the 'de' context have a site_url context setting?
Do you have a base href tag with [[!++site_url]] in the "head" section of all templates?
The exclamation point (!) is necessary for multiple contexts.
i put now "Load only" for the Resource Group to Anonymous Group and i receive now an "Error 401: Unauthorized" if i login to the "de" context.
on "web" context works everything
Try Load, List, and View.
You still haven't answered this: Are you using a plugin or a virtual host (or some Extra) to route users to the right context?