cannot save more than 1 image

Hello!
I was looking for a plugin to insert in a widget, the widget will stay on the right sidebar and the plugin has to show some images (like an automatic slideshow) with a very short text under it, and eventually a link to an internal page.

I’ve been trying to set up this plugin… BUT!
the first image+caption was ok (image size 110 x 110 px).
But the second image won’t save. It says: “Validation échouée. Un ou plusieurs champs sont requis.”, but when I try to re-add a the image (or another one) is says the same.

I’m using WP 4.5.3, and this is my website http://www.letturaolisticadellamano.it/

Please help!

https://wordpress.org/plugins/cvmh-simple-slideshow/