You will need to modify the line 476 of framework/framework.php file –
add_theme_support('post-thumbnails', array('post', 'page', 'portfolio', 'showcase_slide'));
to include the custom post type of this plugin. Since I do not have the source for this plugin, I am not sure what the custom post type is named as. The author of the plugin should be able to tell you or you can find out by checking for references to register_post_type() function in plugin code. Thanks.