I'm having a problem trying to access ftp sites on my PC.

I get the following error when trying to open the connection (using
DOS):
Connection closed by remote host.

If I disable my Windows Firewall, it connects through OK.
I have checked that FTP is enabled on the exception list on the
firewall.
I've also tried using SmartFTP. It is also on the exception list, but
I get the same problem.

I don't really want to turn off my firewall every time I need to FTP.
Does anyone know what else I can change to try to get this to work?
I'm pretty certain that this worked fine a few weeks ago, and I
haven't changed anything dramatic on my PC since then.

Thanks

Ivan