Display Galleries tabs empty

Hoi Nextgen gallery adepts,

Just dicovered that there is a special page for the Nextgen-gallery plugin. So want to try if someone can find a solution for my problem.
I am working with WP 4.1 and the theme is Customizr.
Since almost a week I have been struggling with the Nextgen-gallery plugin. Searched the whole internet and your forum, but could not find the solution.
All of the gallery’s are made and I can see them. And I can link them to the pages.
Everything seems to work fine.
When I try to insert a gallery in a page, I can open the tab “Display Galleries”.
I can also see the different labels (for ex: Select a display type, What would you like to display, …. and so on), but they are empty.

Hope somebody can help me.

grtz,
jef

P.S.: – already uninstalled and re-installed the plugin. But did not help.
– I did check the other plugins, and so far …. no problems with those one’s.
– Changed to 3 different themes and still the same problem.

HerHereby the link to: http://jefvandejumenas.wc.lt/

https://wordpress.org/plugins/nextgen-gallery/