Thumbnails not showing

I am having problems getting thumbnails to show. When I go the category of posts, the thumbs are there on the archive page so thumbs exist and work. Here is my shortcode for mycat post category on a page:
[catlist name=mycat thumbnail=yes excerpt=yes]

Do I have to add the code to my functions.php that is referenced in your other notes page?

http://wordpress.org/extend/plugins/list-category-posts/