I only set a general password in the settings so no guests can view the zenphoto gallery. And I'm logged in as admin and also only can see above album thumbnails ! So whats wrong here?
I have it!!! In settings > picture > there was (german) "Schlossbild verwenden" active. So when choosing a general password in zenphoto this causes this lock symbol thumbnail.
Set this to inactive and now I have my thumbnails back. Thanks!