Images not showing when clicking in gallery

Hi, I was about to update my photo club’s website by adding more images from the last couple of months but have just found out that i can add them to a gallery but when I click on the individual photo in the gallery, it just shows a black screen with a cross at the left button corner but no photo!

It is the free version on this website.

The page I need help with: [log in to see the link]