I set up the Crosswords Pkg all right on Joomla 3.6.2

Then I set up a categorie and after submitting it was moved to a blank page: ..../index.php?option=com_categories&view=categories&extension=com_crosswords

the Back button helped and I was able to create a crossword puzzle from the frontend, solve it and also get the notification as "solved" below the crossword - all works fine

however I am not able to add more categories, for I still only get a new black page when I select that option. reinstalling the pkg has not helped.

any ideas?