Well this one threw me! I was trying out the new custom post types in WordPress 3.0 RC1 and could not work out why mine wasn’t working even when I copied an example from the web and only changed a few things. It turns out that there is a limitation in the naming of post types – they cannot have a name longer than 20 characters! If you use more than 20 characters, the “Publish” button becomes “Submit for Review” and if you submit, you get the dreaded: Are you sure you want to do this? Please try again.