UPDATE: Next time I went to the page, it was okay, I could post.
It also happened to me at Soompi. They first said they banned me (for no particular reason, as I never post nasty stuff). I wrote a fiery mail complaining and said "no, we didn’t actually ban you, it’s a glitch, you have to make a Soompi account. So apparently now to post to Soompi Disqus login is not enough. They asked me to make a Soompi account (they chose my username and stuff) and login every single time. Of course I never comment there anymore, why go to all this trouble?
Disqus is really buggy, ya know? So many times, although I’m logged in with my Viki account, it says I have to authenticate my login going to the Disqus website. When I do that, it considers me a different user and I cannot even edit or delete my own messages!
This has happened to me as well but I figured out what happened…at least for me anyway.
Apparently, if you sit on a page to long and then try to post something you will get that message. I fell asleep watching an episode and when I woke up I just picked back up watching where I left off but soon wanted to make a comment. That’s when I had the problem but refreshed the page and the problem went away.
Don’t know if this happened to you but it is one possible explanation.