Looks to me like your login code is not working properly, because the cookies don't match. You'll need to look into that first.

My guess is that you're hitting something that's common but not usually documented: the site looks for "browsers" that aren't one of the recognized user agents, and sends them through a different flow that often does something different than the standard one.

Try setting $mech->agent_alias('Windows IE 6'); before logging in. Then dump your cookie jar with Data::Dumper and check that you have the same cookies as in your captured with-the-browser example.

You may also want to supply the button argument to the submit_form() call. This supplies the button that was "clicked" in the POST; the backend may respond differently if it doesn't get this data.