Can't Login Remotely

I have a serious problem. The owner of the company can't login remotely. I have tried about everything I know to do, but the computer isn't asking his for a username and password to access the website. It keeps telling him he is not allowed access with the credentials he has provided. Do I need to tell him to delete his history so it will not try to provide a u-name and p-word? Any help would be appreciated, and I thank you in advance for any help given.