I am following the tutorial and adding an Authors section similar to the Staff page:
http://doc.silverstripe.org/doku.php?id=tutorial:2-extending-a-basic-site

I have created a holder and custom page type under them. The fields build and add correctly in the CMS, however the Image tab iframe has a caller error that doesn't make sense to me. The PHP call is_subclass_of is throwing a warning that "Unknown class passed as parameter".

This is a bizarre error as the class it is complaining about is finding my AuthorPage class under DataObject. Obviously the AuthorPage class is being included as I can create pages and work with it. Why would the Image type interface be blowing up on this?

Edit: This has been solved, see the second post

Code:

<?php
/*
 * This is for individual Author entries
 */
class AuthorPage extends Page {
    static $db = array(
                        'Name'  =>   'Text'
                    );

    static $has_one = array(
                          'Photo'   =>    'Image'
                       );

    /*
     * Add our custom data bits
     */
    function getCMSFields() {
        $fields = parent::getCMSFields();

        $fields->addFieldToTab('Root.Content.Main', new TextField('Name'), 'Content');
        $fields->addFieldToTab("Root.Content.Images", new ImageField('Photo'));

        return $fields;
    }
}

class AuthorPage_Controller extends Page_Controller {
    
}

/*
 * Holder for all Author Pages
 */
class Authors extends Page {
    static $db = array();
    static $has_one = array();
    static $allowed_children = array('AuthorPage');
}

class Authors_Controller extends Page_Controller {

}

?>

Error Trace
Attached

I figured this out, it was merely me being stupid.

The way SS works with manifesting it's includes relies on the filename / directory location. I was being lazy and put both the Authors and AuthorPage classes in the same file thinking "its just a plain old require_once somewhere". Wrong!

If you get this error your file and class name do not match somewhere.