I'm using Twenty Twelve theme. I' ve checked its functions.php file and it's calling add_theme_support( 'post-thumbnails' ) (I think in a correct way). I've checked that I haven't more than one Api call in the code. I've installed plugins but any of the conflicts list. I have readean every post in this forum support and I don't find the key. I have tried RC1.10-4. I don't know a lot of about wordpress, custom types or thumbnails.
I am determined to use this plugin :-).
Thanks for your attention and sorry because my english :P.