I have a ftp server behind a load balancing firewall. When I have the ftp server infront of the firewall then I don't have any problems connecting to it from a work station. When I have the ftp server behind the firewall I get this error:

connection refused; the server would not accept an FTP connection

I know the connection from the client is getting to the ftp server behind the firewall as I can see it when I am listening from the ftp server on port 21.
Is it possible that it is trying to connect via some other method that is not getting through the firewall that is not on port 21.

Here is the whole printout of the transaction between the client and the server.

Finding Host ftp.server.com ...
Connecting to <ip address>:21
Connected to <ip address>:21, Waiting for Server Response
220 hostname FTP server (Version wu-2.6.1-20) ready.
Host type (1): Automatic detect
USER ftp_user
331 Password required for ftp_user.
PASS (hidden)
230 User ftp_user logged in.
SYST
215 UNIX Type: L8
Host type (2): UNIX (standard)
FEAT
500 'FEAT': command not understood.
PWD
257 "/home/ftp_user" is current directory.
TYPE A
200 Type set to A.
PORT 10,10,0,5,4,79
502 Illegal PORT Command
Port failed 502 Illegal PORT Command
PASV
227 Entering Passive Mode (10,10,1,9,4,242)
connecting data channel to <ftp internal ip address>:1266
Substituting connection address <ip address> for private address <ftp intrenal ip address> from PASV
connection refused; the server would not accept an FTP connection.

I figured it out. It connects on port 21 and it connects on a non-private port.