Thread:Extension talk:SmoothGallery/external pictures doesn't work

hello, I've installed SmoothGallery on MW 1.15.4 and then I enabled $wgSmoothGalleryAllowExternal, I put it to true and put the following code : http://website.com/picture.png|description Result, SmoothGallery gives me the following error : '''SmoothGallery error:No images were found in this gallery. Make sure all images requested exist. The following images were not found: '''

where's the problem? how do I do fix that? thank you.