Put use LWP::Debug qw(+); at the beginning of your script and see what happens, if you have not done it yet.
I have been using been using LWP::UserAgent for browsing dozens of sites. I just do $ua-cookie_jar(HTTP::Cookies->new) in my LWP::UserAgent setup and it�s an absolute no-brainer. Just forget about cookies, but I have to go through the right sequence of urls. If you cannot POST an url succesfully, maybe some parameter is missing or wrong.
