[Plugin: Slideshow Gallery] fatal error

When trying to set the order of the slides i get the follwing error:
Fatal error: Class ‘GalleryPlugin’ not found in /home/content/74/5970774/html/insideoutsupercenter/wp-content/plugins/slideshow-gallery/slideshow-gallery-ajax.php on line 7

http://wordpress.org/extend/plugins/slideshow-gallery/