When this happens, it's usually because of a login issue, such as trying to log in to Disqus from a separate account than your AG account. And sometimes Disqus just decides to ban people. Since this involves a ban and, as such, is private info, you'll need to contact the admins directly. Check out the Disqus Comments help page. There's a link there to dispute the ban directly, which shouldn't be a problem.
