accessing ftp site through explorer

ok, we have a ftp site that is hosted by our ISP. All computers but one can just type the address of teh ftp server and it asks for login and they access files. But this one machine says it can’t find the ftp server, dns error. It has the same DNS entries and internet setup.
they all go through a DSL modem attached to a switch.

any ideas? I am putting a lot of points up for a quick answer, this will be closed by the end of the day.

Bill