certian user unable to logon to new FTP server

Last week we new a new Windows Server 2003 box online taking the place of our old NT 4.0 box which served as a FTP server along with a web server for my company. Most of the people who use the FTP site have had no trouble getting on the site.

I do have two users who are unable to get on the site. I have personally talked to one of the users he has told me that he is using Windows XP and IE 6 and was able to get onto the FTP site before when it was on the NT box. Also he is able to get onto his office FTP site which is hosted by a separate company.

I know his security settings in IE are set to medium and the advance tab is set to ?Use Passive FTP (for firewall and DSL modem compatibility)?.

Any ideas?