Ok, I can reproduce the problem with the 'Sorry, comments are closed for this item':
I have included an option to overwrite the 'Allow comments' status of the guestbook site. This option is set automatically. With this option enabled the comment form is shown, but it looks like that posting comments still don't work. I will try to fix that issue as soon as possible.
I the meantime you can fix it with the following workaround:
Edit your guestbook site and enable 'Allow Comments' in the Discussion options of the site.
For the second issue (double comment box) I don't have an explanation yet. Can you please check if the second box is in the article or in the comment div?