I have two custom post types on a single site install - exhibitions and classes. Both have 'support' => 'thumbnail' enabled, AND I have
add_theme_support( 'post-thumbnails', array( 'post', 'exhibitions', 'classes' ) ); in functions.php.
I also have two versions of the site - one on localhost, and one live, which I copied from the localhost version very recently. In the localhost version, the featured image metabox shows up just fine for both custom post types. There's different content in the live version, but otherwise, the ONLY difference in the entire file structure is that I have Google Analytics installed and enabled. Any ideas?
By the by, I'm using Nextgen Gallery (version 2.something) to generated the featured images for the custom post types. But again, it works just fine for both CPTs on the localhost version.