This has been a bug for the last few versions I believe. I am trying to find the original thread on this, I don’t believe it has been fixed yet.
I’m not sure what happened to older messages, I can’t seem to bring them up. Anyway, try to roll back a few versions. You can use the WP Rollback plugin to do this easily, make sure to make a backup first.
It looks like support for older style themes was dropped. From my testing (I haven’t checked the code) – if a theme does not use the WordPress function comment_form() to generate the form fields, then this plugin will no longer work. It won’t error anywhere, it just won’t display the ‘subscribe to comments’ output.
To be fair, the comment_form() function has been around a long time, so it’s not clear how many themes this would affect. But a warning would have been nice 🙂
