FTP Problems with a cable modem

I am trying to solve a subtle FTP problem.

When my son switched to a new ISP (using an one-way cable modem),
he can no longer FTP into my server.

He can still telnet OK and browser works OK -- but he can't FTP to my server.

This is puzzling -- because he can -- still FTP to his others sites --OK
(one is unix using NcFTPd, the other is windows server), but not to my server.

My server is Red Hat Linux release 6.1 with version Apache/1.3.9
(note: I am using Version wu-2.6.0(1) FTP server)

His FTP program never connects -- it just times out -- he has tried
other client problems as well --  with the same result.

I had a number of friends try it out -- and It always works OK for them and
of course, OK for me as well going thru my local ISP.

Perhaps, somebody else -- has had a similar problem or maybe
a suggestion!

Thanks,
David Green
http://greenspider.com

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