Newbie ftp problem

I was going to try and use ruby to transfer files to an FTP site so I
figured I would try some simple code in the irb.

ftp = Net::FTP::new('my.url.com')
ftp.login('login_id','login_pass',nil)
ftp.chdir('data')

all goes fine but at this point I have tried all of the following and
get the same errors

files = ftp.list('data')
files = ftp.dir('data')
files = ftp.dir(dir = nil)
files = ftp.nlst('data')

Net::FTPPermError: 500 Invalid PORT command.

I know that there are files that should have been listed.

I have Googled the error and looked on the news group to get a solution
and haven't found one or was not smart enough to understand the one
that was given.

Any help would be appreciated.

Len Sumnler