I'm using the Thesis theme and can't get thumbnails to display with the post excerpts. I read through some posts here (and on the Thesis forum) and removed the "s" from "thumbnails" and added this function to my custom_functions.php file:

 if(!function_exists('get_post_thumbnail_id') && function_exists('add_theme_support')) {
   add_theme_support('post-thumbnails');
}

Here's what the shortcode looks like on the page:
 [catlist excerpt=yes author=yes id=56 orderby=date order=desc thumbnail=yes]

Can't share a site link because of copyright issues. Thanks in advance for the help!