I did not made any changes on the stylesheet, only i perform a backup of the wordpress site, after I updated the WordPress version to the latest (3.3.2) and also I did the update to the latest version of the Image-Store plugin (3.0.4).
Please, you can check over here selecting one Gallery and when you go to see in particular just one photo contact, is showed with a wrong Image-store lightbox, just a few time work good.
The site is: http://venefoto.com/fotobill/?page_id=12
Thanks in advance. All the best.
Gio