I’ve checked that link you provided and it still doesn’t work. Like I said, the form worked on my local dev site using MAMP, but when it’s on the live server it shows that. Are there certain server settings I need?
Edit: I’ve added a comment to the Spanish side of the blog and the error is there. The /es/ is the same install. I’m just using WPML so I only have to manage one blog with blog languages.