Hotmail website and ISA Server

Hi all, We have a client running an sbs 2000 server. Whenever anyone tries to access the hotmail website, they can get to the main login page, but after logging in the mail page never loads it eventually times out, with the message that the gateway has lost the connection, we have the same problem for a few people who (for whatever reason) try to access the aol.com website for their personal mail. No other websites are affected and I have yet to find one besides these two that have the same result. Currently packet filters are set up to allow all ip traffic but these two sites still do not work, any help would be appreciated. Thanks