image resizing

I have got a problem with images.

I installed the lightbox plugin and in the beginning this works at the images.
In the meanwhile I make some changes on different places but now it do not work at some places.

It works at the PAGES
https://www.abdijtorenbuurt.nl/worldpress/about/

But it do not work at the MESSAGES https://www.abdijtorenbuurt.nl/worldpress/

When I go to the configuration of a posted PAGE
https://www.xxxxxxxxxx/wp-admin/post.php?post=2&action=edit
I can change the size of the images by using the mouse.

When I go to the configuration of posted MESSAGE
https://www.xxxxxxxxxx/wp-admin/post.php?post=52&action=edit&message=1
I cannot change the size of the immage.