Log in permission error

I have just created a new user and set him up on the exchange server. The problem is, when I try to set him up at his workstation, I receive an error message – you do not have permission to access this server.

I have had another person at the office check the setting etc and everthing is correct but the user cannot gain access to email. I have logged in using my account and was able to gain access but when I use the user account there is still no access. The computer is running Windows XP.
Does anyone have a suggestion?