The problem stated here: http://www.nimble3.com/nimble-portfolio-free-filterable-jquery-porfolio-wordpress-plugin/#comment-343
Solution is simple, just add 'portfolio' in the array of post-types.
e.g. array ('post', 'page', 'movie'); will become array ('post', 'page', 'movie', 'portfolio');
If you still face this issue, it means it add_theme_support('post-thumbnails'); is called by another plugin. You need to fix that as well.
