Lightbox 2 doesn't recognize image and its broken

Hello,
I am using lightbox2 module on Drupal 7. I have tried to setup a fixed size 300x300 but then my lightbox gets broken with this message : http://imgur.com/5iEzKxI
I have all images saved, so he's not loading them or not working correctly. Anyone have idea what might be causing this ?
Thanks, Michael