Works for me. You do have many packages explicitly use'd that don't need to be, It will work just as well with:

use LWP::UserAgent;
use HTTP::Request;
[download]

With just that, the page is downloaded successfully. That said, the contents do appear to be attempting to display some sort of error message via Javascript.

It looks like the URL needs some addition GET parameters. You need navGraph=Login&foo=bar&klong=sproink and so on. Exactly what parameters are needed will require a little more detective work on your part.