WP-FFPC trying to cache content that no longer exisits

Hi,

That is most probably not the plugins fault but WordPress itself.
This is the code what lists the urls to be pre-cached:

/* get all published posts */
$args = array (
	'post_type' => 'any',
	'posts_per_page' => -1,
	'post_status' => 'publish',
);
$posts = new WP_Query( $args );

/* get all the posts, one by one  */
while ( $posts->have_posts() ) {
	$posts->the_post();

	/* get the permalink for currently selected post */
	switch ($post->post_type) {
		case 'revision':
		case 'nav_menu_item':
			break;
		case 'page':
			$permalink = get_page_link( $post->ID );
			break;
		case 'post':
			$permalink = get_permalink( $post->ID );
			break;
		case 'attachment':
			$permalink = get_attachment_link( $post->ID );
			break;
		default:
			$permalink = get_post_permalink( $post->ID );
		break;
	}

	/* in case the bloglinks are relative links add the base url, site specific */
	$baseurl = empty( $url ) ? PluginUtils::_site_url() : $url;
	if ( !strstr( $permalink, $baseurl ) ) {
		$permalink = $baseurl . $permalink;
	}

	/* collect permalinks */
	$links[ $permalink ] = true;

}

as you can see it uses the built-in options WordPress provides.

Is the post in the thrash or is it fully deleted?

Are you using any kind of persistent object cache?
Could a MySQL query cache be involved?

I honestly have no idea why this is happening.
Could you please try to query the db directly to see if the post is there or not or has any clues?

this last error seems to be an issue with the theme that’s trying to utilize the wordpress internal cache functions.

wordpress has it’s own cache layer, which can be enabled by define(‘WP_CACHE’, true) in wp-config.

If they are not checking for this in the theme and trying to use the cache_set/get/etc functions, this might result the error, but this is my opinion, since I don’t know the actual code.