[Plugin: WP Wall] Can't submit comments (Please fill in the required fields)

I have an issue with WP-Wall and the comments form. First time, I posted to the Wall, it worked fine but now for some reason, No matter what I do, whether I’m logged into WordPress or not, I get the same error:

Please fill in the required fields.

But all the fields are in fact…required. Why is that happening? What should I look for in the settings or code?

Page in question: http://rockshopnroll.com/wordpress/category/scene/