Can't programmatically add page content to page

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I have built a package that includes the following XML in content.xml. This sets up the page type called "TV Show" in my C5 installation. When I add new pages using the C5 Dashboard, it all works.

<?xml version="1.0"?>
<concrete5-cif version="1.0">
    <pagetypes>
        <pagetype name="TV Show" handle="tv_show" is-frequently-added="1" package="tv_shows" launch-in-composer="1">
            <pagetemplates type="custom" default="right_sidebar">
                <pagetemplate handle="right_sidebar"/>
            </pagetemplates>
            <composer>
                <formlayout>
                    <set name="Details">
                        <control custom-template="" custom-label="Show Title" type="core_page_property" handle="name"/>
                        <control custom-template="" custom-label="URL Slug" type="core_page_property" handle="url_slug"/>
                        <control custom-template="" custom-label="Summary" type="core_page_property" handle="description"/>
                        <control custom-template="" custom-label="Synopsis" output-control-id="6y4mB58T" type="block" handle="content"/>
                        <control custom-template="" type="core_page_property" handle="publish_target"/>


However, when I add the page programatically using the Page API, I see a blue box with the following message on the page:

The Synopsis page type composer form element will output its contents here (Block ID 11)


In the Composer view, I see this message:

include(<snipped>/concrete/blocks/core_page_type_composer_control_output/composer.php): failed to open stream: No such file or directory


What am I missing here? Are there extra steps I should take note of when adding new pages programatically?

MrRonbot