I use OpenID plugin 3.3.3 on a WordPress 3.3 powered site hosted by hostgator.com.
Every time i trying to login to my site with OpenID - i see an error message:
"OpenID login failed: Invalid openid.mode \'<No mode set>\'"
Here is a part of the conversation i had with the Hostgator support:
(1:18 pm) [Cody B.] Yep, I've just whitelisted the rule I think it is, can you check again if it still occurs after clearing your cache please? The following support page shows how to empty your cache with specific instructions for most browsers: http://support.hostgator.com/articles/specialized-help/how-do-i-clear-my-web-browsers-cache
(1:25 pm) [KaiSD]: I've cleared the browser cache, and still see the same error message.
(1:31 pm) [Cody B.] I see. I'm afraid I cannot guarantee to be able to get all WordPress plugins working. I've confirmed it's not a mod_security issue and there doesn't seem to be any other errors generated. You may need to contact the plugin developer directly. I'm truly sorry for this inconvenience.