I'm going to guess that that long hex string is some sort of session identifier and you're probably missing a temporary cookie that's set to expire when your browser quits, or perhaps coming from a different machine than the session was started from.

In either case, you're probably going to be better off using WWW::Mechanize to go through the site's login page then navigate to whatever data you're trying to retrieve. Or see if they don't have some sort of SOAP/XMLRPC/REST-y interface for queries that you may can hit directly.