Outlook anywhere prompting for password

I have Exchange 2003 running on a small business server with Outlook 2007 clients. 6 existing users can successfully connect using outlook anywhere ussing http with basic authentication. I added 2 new users, connected to Exchange connected to the LAN, enered the same connection info as existing users. The problem is the when the 2 new users are out of the office, Outlook will not accept their username/password to connect to exchange.
This has me stumped, any ideas?