publish_post action not hooked?

I have your plugin installed and working correctly, but I am trying to make my addon work with it.
I add the metabox to post type “content_block” and that works.
But the action I am binding to is “publish_post” which does not seem to be called when the content block is published.

Can you please tell me which action I should be using?
Thank you

http://wordpress.org/extend/plugins/custom-post-widget/