Related to windows 2000 exchange server

I have configured a user known as Michael with an user account with a mail box on the exchange server 2000. He is able to access his mailbox and exchange mails with other users on the network

On his windows 2000 professional he has created a dial-up connection and whenever he tries to connect to the exchange server with outlook web access the dial-up connection pops up asking the page is offline try to connect. I tried to add the address in the exceptions box on the internet explorer, however the result is same. when i delete the dial-up connection the explorer connects to the exchange server.
How can i solve this problem of Michael to allow him to connect to the exchange server using outlook web access.