[Plugin: Facebook Comments for WordPress] Unknown Error

I’ve been using facebook comments for wordpress without problem. But suddenly it started asking all my site visitors to fill out captcha before every comment and they have stopped commenting on news stories.

It shows something like that;

Security check
Captcha required
Unknown error

This is new and I don’t know what to do next?

My site is here

http://wordpress.org/extend/plugins/facebook-comments-for-wordpress/