Error: Something has gone horribly wrong

Here’s what I have in one of my single-custom_post_type.php files – it appears to be ajax related as when its disabled the content will show. However, with Ajax enabled, it appears to be trying to load the content, then spits out “Something has gone horribly wrong”.

Unfortunately I require the use of Ajax on this piece of hidden content. Any ideas?

<?php
$passwordcontent = "<h2>Testing the hidden content</h2>";

echo do_shortcode('[content_protector password="test4" identifier="1234" cookie_expires="1 hour" ajax="true"]' . $passwordcontent . '[/content_protector]');?>

https://wordpress.org/plugins/content-protector/