We've had computer issues recently and had a new firewall installed, which may be the cause of my problem.

Anyway, I tried to log in to my Coffeecup program and get the following error:
The remote server denied login. Your username and/or password is not correct, or attempting more concurrent connections than the server allows. [67] Additional information: Access denied: 530.
Server has replied: [530] Login authentication failed


Can you direct me as to what to do?

Which of the 30 odd Coffeecup programmes are you talking about?