invalid PORT command

[Gabor Gludovatz <ggabor@sopron.hu>]

Hello,

there is an NT FTP server with private IP (192.168.0.240) behind a
Debian, and on the Debian the port 90 is forwarded to the nt's port 21
with redir. If I try to connect
to the Debian's port 90, I get connected to the NT, but if my ftp client
tries to download
something or even do a directory listing, the nt's ftp servers says:
'invalid port command'.

So, the server (the NT) is masquaraded, not the client, that's why I use
PORT instead of PASV.

My FTP client (Internet) --> Debian (masq firewall) --> NT FTP server
(private IP)

Cmd: PORT 63,112,201,195,4,136
500: Invalid PORT Command.

Does someone know, what to do in this case?

The ftp server is Microsoft FTP Service (Version 5.0).

Thanks,
  Gabor