Outlook 2003 cannot connect to Microsoft Excjange Server 2003

Hello
I have 30 users or so which have a problem connecting to Microsoft Exchange server 2003. They are all using Windows Xp service pack 2, with all the latest updates.

They get the following error, “failed to connect to microsoft exchange server, do you want to do the following. Retry, Work offline or cancle.”

Some clients can click on the network icon and repair their IP setting and it then works as long as Outlook is shut down. Others have to restart the computer several times before it comes back.

Has anybody got any ideas as to what i can try next?