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The comment system is using captcha and it is slightly more restrictive than it used to be... because we had in excess of 12k spam comments put on stories in about two and a half months earlier this year. So after spending the time cleaning it up, I had to set it to be more restrictive. If your browser is blocking access to the captcha check, you're not going to be able to make comments on the stories directly. You can still post comments in the forums thread for any given story... in fact, that's 'ideal' because comments directly attached to stories can often be missed entirely once a story is more than a couple months old... because most people (even the authors) don't get notified when new comments are posted... so once they stop looking actively, new comments can be completely missed. But with the forums, its easier to see new posts (and to subscribe to a thread to get updates when someone comments).