This demo is using [thumbnailgrid posts_per_page="999" gridwidth="350px"]. Setting posts_per_page overrides the default number of posts that display. As of version 2.1, gridwidth sets the size of the grid. Go to the Admin panel, click on Settings, choose “Readings Settings”. On this page there is a setting labeled “Blog pages show at most”. This is normally set to 10 and controls the maximum number of posts that display on a blog page. This plugin is not designed to display pages of post thumbnails. If you have more than 10 thumbnails you can get around the problem by using the posts_per_page setting. If you set it to 999, all of your thumbnails will be displayed, as long as you do not have more than 999 posts. Additionally, you can control your display if you make use of categories!