We have switched to the more common blog commenting system disqus as the previous comment system we used worked via the forum's database.
However it worked great the creator of this bridge software has stopped supporting it and recently no updates have been executed which brings besides some nasty bugs also security errors.
In order to comment you need to log into discuss by creating a free account or via facebook, twitter etc. On the right top of the comment area you should be seeing a Login button.