I can answer this, because I was doing exactly the same thing :)

The form will not work unless you have the session cookie set. Perform a GET on the page, then ensure you've got that cookie in your cookie jar when you submit the form.

I couldn't be bothered to write code for this though, so I just created two bookmarks on my toolbar and clicked them quickly in succession ;-) One gets the page, the other loaded a form that autosubmitted itself with JS.

.02

cLive ;-)

ps - you can see the cookie issue by navigating to the page, deleting your session cookie, then submitting the form.