Notice when activating the plugin

Notice: Undefined index: restore in /var/www/stoessel-media.ch/www/wp-content/plugins/post-gallery-slider/post-gallery-slider.php on line 42

I’m using WordPress with multisite and having this notice when i activating the plugin. Please help me. Thanks.

http://wordpress.org/extend/plugins/post-gallery-slider/