Specific User Cannot Post Comments

One of the frequent visitors to my site (http://www.raddue.net), cannot post comments anymore. I just recently upgraded to 1.5.2 after being at 1.5.1, but this problem started before the upgrade to 1.5.2. Other people (including myself) can post comments just fine. When he tries to, the site tells him he isn’t logged in, then sends him to the Dashboard (he’s a co-author) which tells him that he is logged in.

He can post new articles, he just can’t comment in them. He’s tried dumping his cache, history, internet files, restarting, he’s even tried different computers on entirely different IP addresses and he gets the same problem every time.

Help. 🙁