Outlook Web Access

Hi
Can anyone help i wonder. I have recently installed OWA onto my exchange 5.5 server and have also installed the option pack as well. The server has exchange SP3 installed. i want to use this across my internal LAN. When trying to access my inboxacross the LAN i enter my credentials and then i get a error saying “unable to get Inbox”. I have had no experience with this and am trying to use this as a learning exercise before it is installed for internet access. At the moment i trying to findsome troubleshooting doco relating to this but am finding it rather thin on the ground. If anyone can help i would really appreciate it.. Thanks in advance