I have been using OpenID as one of the ways someone can login and comment on my blog. It has been working fine and then suddenly today it stopped working. Every single time someone has tried to login using it, they have received a 403 Forbidden. They said they have received it using IE and Firefox.

Any suggestions?

UPDATE 11/14/2008: I reinstalled MT 4.21 and it is still happening. I can login to comment with MT and Typekey ... but not OpenID. What could be causing that?