Port Mapping Filezilla FTP Server

Question

I just got a new AirPort Extreme Base Station (802.11n). I must say, I'm pleased for the most part. I'm having an issue with remotely connecting to my FTP server inside the network though.
Setup:
The whole this is connected as follows:
Cable Modem - AEBS - Wired Windows PC
On this windows PC I run an FTP & HTTP server. Both are functioning properly as they always have, both on the localhost and within the network.
The HTTP protocol is working fine. I have port 80 mapped to my PC's static IP of 10.0.1.100. I can browse my hosted site from a remote PC no problem.
Yet, from a remote PC I am unable to fully establish FTP communication. I have port 21 mapped to my PC's static IP as well. Communication seems to be happening; the remote PC gets prompted for their username and password. Shortly after (within a timeout time), the FTP server replies that it cannout open the data channel.
Data:
Here is the Remote PC's log of the FTP session:
Status: Connecting to $server.com ...
Status: Connected with $server.com. Waiting for welcome message...
Response: 220 $greeting
Command: USER $username
Response: 331 Password required for dave
Command: PASS $pass**
Response: 230 Logged on
Command: SYST
Response: 215 UNIX emulated by FileZilla
Command: FEAT
Response: 211-Features:
Response: MDTM
Response: REST STREAM
Response: SIZE
Response: MLST type;size*;modify;
Response: MLSD
Response: UTF8
Response: CLNT
Response: 211 End
Status: Connected
Status: Retrieving directory listing...
Command: PWD
Response: 257 "/" is current directory.
Command: TYPE A
Response: 200 Type set to A
Command: PASV
Response: 227 Entering Passive Mode (10,0,1,100,16,141)
Command: LIST
Response: 425 Can't open data connection.
Error: Could not retrieve directory listing
Solutions Attempts:
I have tried mapping the FTP data port (20) to the server's static IP to no avail. I even went as far as setting the server as the default host (DMZ); this didn't work either.
Am I looking at a fresh firmware bug here or am I missing anything? Thanks for your help.
P.S. No changes have been made on the server and every other no name router I've used has successfully port mapped the server; it's definitely the new hardware.
Windows PC Windows XP Pro
Windows PC   Windows XP Pro  

Answer 1

1. Try to connect to your FTP-Server in AKTIVE-Mode,
it's a setting in your FTP-Client
Most all FTP clients are defaulted to passive mode, and I want to connect without asking all users to change their settings.
Previous routers did not require anything like this, why would this new base station obfuscate the setup?
2. Don't use the same AirportXtrem internet
connection (for testing your FTP-Service) where is
your FTP-Server behind. I don't know why, when I try
to establish a connection I could not go out and come
back through my AXtrem on the same way.
Try it with a Modem, UMTS or with another internet
connection.
I don't know exactly what you're talking about. Please explain better or with more details.
Windows PC Windows XP Pro