Can’t register users

I set the forum up on the server and it seems to work fine. I have all admin functions. When a new user registers they get an email notifining them that they have been registed (so far so good). The problem is the link in the email back to my forum which askes them to confirm, causes a white "page cannot be displayed" error message in the browser instead of the confirmation page. Is this a database write problem or what?  Help!!!