I've heard some people say that they think you may have to reinstall the certificate and that may jump start Siri again. Just a guess though, I have no proof or good reasoning to believe that would help. I've only been using siriport since yesterday.
Also, there's a website you can check for the status of the server. Sometimes it's just a little overloaded, and will work again when it slows down.
I don't remember, I'm not using siriport now since it stopped working the second day I had it. But if you have it installed, there's a link to it somewhere either in the install process or in the settings for the app.