Plugin crashes my gallery

Hi,
I have a problem. I’d like to have an image gallery (thumbnails) and below listed posts which have have the same cattegory. Gallery works correctly on sites where ypur plugin is not used but doesn’t work when posts in page shortcode is added.
Instead of thumbnail gallery like here:
http://unipics.esy.es/portret/
I see only one thumbnail.
This is a problematic page:
http://unipics.esy.es/wydarzenia/

For gallery I am using NextGen.
Is there a way to work it around or is it a problem with Nextgen?
Thank you for your help.

https://wordpress.org/plugins/posts-in-page/