Hi Hermann,
you caught us right in the moment were we wanted to move the forum (because a lot of stuff is not properly working here).
Since we already migrated the database, is it possible for you to repost this question to the new forum at:
forum.ngsolve.org
You should be able to log in there with the same username + password (so you can also be one of our first test users for the migration...

)
Best
Christopher