Post thumbnail is not shown in wp-admin

I figured out it was because of an script that was delivered with the Options Framework. There was a little piece of code in my functions.php which caused wrong javascript to be loaded.

When you are having the same problem, be sure to search for something like wp_enqueue_media(); or something of the following script, comment out and try to upload a thumbnail.

if( function_exists( 'wp_enqueue_media' ) ){
    wp_enqueue_media();
} else {
    wp_enqueue_style('thickbox');
    wp_enqueue_script('media-upload');
    wp_enqueue_script('thickbox');
}

Thanks for all answers, though.