Because of excessive use of abusive contents in free domains like .co.cc, Facebook has banned these domains. Upon posting a comment with .co.cc, Facebook reports error message. Not only in comments, .co.cc is banned in all of the service provided by Facebook.

For example, one of the plugin by Facebook, Like button does not work, it shows error.

Going further, Facebook reports that the blog as abusive to Facebook users.

If you are creating your website in .co.cc, you won’t be able to use any of the Facebook services.

So, why Facebook banned .co.cc? 

Actually, .co.cc is a free subdomain provided by www.co.cc. Since it is free, anyone can create an account for them and register up to four free .co.cc domains. Among all the subdomains of .co.cc, most of them are found to contain abusive contents. Probably some people might have requested Facebook to ban domain name ending with .co.cc.

Mostly, co.cc domains are used by proxy servers.  Co.cc’s are perfect for proxies, because they can be created easily and cheaply and then thrown away. And also adult contents are widely being used in .co.cc domains. While there are no one to moderate and monitor .co.cc domains.