I already checked this and its fine.
I have test on an other joomla base on local and it worked, their is a conflict with something but hard to tell. No idea Katia ? If i cannot fix it, i will set u a ticket to be refunded if possible because it's unfortunately useless.

I cannot help you if I do not see the problem... You need to post me again when you get online in order to solve your issue...
According to our Terms and Conditions, since our company is offering non-tangible irrevocable goods we do not issue refunds after the product is shipped.

I understand Katia, and i guess we shoudl be able to fix it.

Here could be some interesting information for you :

this is what i can read on the template systeme check from yootheme cloud :

System Check1 potential issue(s) detected.
Multiple jQuery Libraries found. Please make sure these don't conflict each other.
GARBAGE
/components/com_jce/editor/libraries/js/jquery/jquery-ui-1.8.21.custom.min.js
/components/com_jce/editor/libraries/js/jquery/jquery-ui-layout.js
GARBAGE
/components/com_phocadownload/assets/plupload/jquery.plupload.queue.min.js
GARBAGE
/components/com_phocagallery/assets/plupload/jquery.plupload.queue.min.js
/components/com_sobipro/lib/js/jquery-ui.js
GARBAGE
GARBAGE
GARBAGE
GARBAGE
GARBAGE
GARBAGE
GARBAGE
GARBAGE
/media/k2/assets/js/jquery-ui-1.8.16.custom.min.js
GARBAGE
GARBAGE
GARBAGE
/modules/mod_btslideshow_pro/admin/js/jquery.lightbox-0.5.min.js
GARBAGE
GARBAGE
/modules/mod_btslideshow_pro/assets/skitter/js/jquery.animate-colors-min.js
/modules/mod_btslideshow_pro/assets/skitter/js/jquery.easing.1.3.min.js
/modules/mod_btslideshow_pro/assets/skitter/js/jquery.skitter.min.js
GARBAGE
/modules/mod_k2_filter/tmpl/js/jquery-ui-1.8.16.custom.min.js
/modules/mod_lofk2showbiz/assets/jquery.cssAnimate.mini.js
/modules/mod_lofk2showbiz/assets/jquery.easing.1.3.js
GARBAGE
/modules/mod_lofk2showbiz/assets/jquery.mousewheel.min.js
/modules/mod_lofk2showbiz/assets/jquery.script.js
/modules/mod_lofk2showbiz/assets/jquery.touchwipe.min.js
/modules/mod_minik2/tmpl/newsticker/assets/jquery.ticker.js
/modules/mod_minik2/tmpl/portfolio/assets/jquery.quicksand.js
/modules/mod_minik2/tmpl/simple/assets/jquery.masonry.min.js
/modules/mod_minik2/tmpl/thumbnail-proximity/assets/jquery.proximity.js
/plugins/content/jw_sigpro/jw_sigpro/includes/js/jquery_colorbox/colorbox/jquery.colorbox-min.js
/plugins/content/jw_sigpro/jw_sigpro/includes/js/jquery_colorbox/colorbox/jquery.colorbox.js
/plugins/content/jw_sigpro/jw_sigpro/includes/js/jquery_fancybox/fancybox/helpers/jquery.fancybox-buttons.js
/plugins/content/jw_sigpro/jw_sigpro/includes/js/jquery_fancybox/fancybox/helpers/jquery.fancybox-thumbs.js
/plugins/content/jw_sigpro/jw_sigpro/includes/js/jquery_fancybox/fancybox/jquery.fancybox.js
/plugins/content/jw_sigpro/jw_sigpro/includes/js/jquery_fancybox/fancybox/jquery.fancybox.pack.js
/plugins/content/jw_sigpro/jw_sigpro/includes/js/jquery_fancybox/fancybox/lib/jquery.mousewheel-3.0.6.pack.js
/plugins/content/jw_sigpro/jw_sigpro/includes/js/jquery_prettyphoto/js/jquery.prettyPhoto.js
/plugins/system/cdscriptegrator/fields/uithemecombobox/js/jquery.dd.js
/plugins/system/cdscriptegrator/libraries/cleditor/js/jquery.cleditor.min.js
GARBAGE
GARBAGE
/plugins/system/cdscriptegrator/libraries/jqueryui/js/jquery-ui-1.8.20.custom.min.js
/plugins/system/jqueryeasy/jquerynoconflict.js
GARBAGE

Can you see anything hat could explain the problem ?

I really don't know... This doesn't look like affecting SIG PRO...
Please post me again when you get online...

Katia i have uploaded an alpha version of the website here :

aefe-asie.net/alpha/

It's the alpha version of my website.

It's password protected :
login : admin
password : alpha-aefe

The page with a sample gallery is here :

aefe-asie.net/alpha/index.php/test-gallery

And the funny thing is that on the hosting server, it's working but not locally on my computer !

Thanks for your support Katia

As far as I can see the gallery works just fine in the link you post here...