Yes, I saw that you previously sent us a support ticket, and we replied the following:

We have recently made some changes to the commenting feature. You can find more information about it here:

http://en.forums.wordpress.com/topic/recent-update-to-commenting

[...] If some of your readers contacted you about issues when trying to comment on your blog, please make sure that they are logged in with the same WordPress.com or Gravatar account that is attached to the email address they are commenting with.

Note that if someone leaves a comment with an email address not associated with a WordPress.com or Gravatar account, they won't be required to log into WordPress.com or Gravatar.

I hope this helps!