/includes/thumbs/includes.php – failed to open stream

I recently made a copy of one of our WP sites for development purposes. However, I can’t get it to load.

The error I’m getting is:

Warning: require_once(...../wp-content/plugins/foogallery-premium/includes/thumbs/includes.php): failed to open stream: No such file or directory in ...../wp-content/plugins/foogallery-premium/includes/includes.php on line 21

(….. = removed for brevity)

I checked, and the includes.php file does indeed seem to call that file, and it doesn’t indeed exist.

But then, the exact same file is used on the site proper, and it works there. So what the hey?