Your plugin conflicts with the plugin Kama SpamBlock. I can add only first comment, but when I add a second comment, I get a message "You are a bot or java scripts does not work in your browser". Kama SpamBlock create this error because it blocks the automatic spam. But i am real user and scripts works fine. After reloading the page I can add a comment again, but only one.
So if i use your plugin or Kama SpamBlock separately everything is okey. If you can help you can see Kama plugin in this link http://wp-kama.ru/wp-content/uploads/2010/07/kama_spamblock-v1.3.3.zip