Rights for adding a gallery at frontend

Hi,
I've given a user both front-end and back-end permissions to embed a gallery in an article.
Using the front-end with JCE as the editor, I see a Gallery button at the bottom of the screen.
I click it and choose All.
But the popup that then appears where I have to select a category remains grayed out between the top and bottom.
If I do that through the backend, it works fine.

What could I do to make it work properly on the frontend as well?

\Regards,
Wouter

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