Error 421 can't create socket

[benniegibson]

I've looked at the various entries about this error and cannot seem to find a match for my situation.
Users logging in via any browser cause error 421 socket error. I've configured passive mode (see log and settings below). Any suggestions on other things to try?
Thanks

passive mode settings:
custom ports 21-21 (port 21 is enabled in router)
have tried both "use this IP" with my external IP address as well as referring to http://ip.filezilla-project.org/ip.php

(001041)11/5/2012 10:43:20 AM - (not logged in) (192.168.1.102)> 220-FileZilla Server version 0.9.41 beta
(001041)11/5/2012 10:43:20 AM - (not logged in) (192.168.1.102)> 220-written by Tim Kosse (Tim.Kosse@gmx.de)
(001041)11/5/2012 10:43:20 AM - (not logged in) (192.168.1.102)> 220 Please visit http://sourceforge.net/projects/filezilla/
(001041)11/5/2012 10:43:20 AM - (not logged in) (192.168.1.102)> USER arnie
(001041)11/5/2012 10:43:20 AM - (not logged in) (192.168.1.102)> 331 Password required for arnie
(001041)11/5/2012 10:43:20 AM - (not logged in) (192.168.1.102)> PASS *****
(001041)11/5/2012 10:43:20 AM - arnie (192.168.1.102)> 230 Logged on
(001041)11/5/2012 10:43:20 AM - arnie (192.168.1.102)> SYST
(001041)11/5/2012 10:43:20 AM - arnie (192.168.1.102)> 215 UNIX emulated by FileZilla
(001041)11/5/2012 10:43:20 AM - arnie (192.168.1.102)> PWD
(001041)11/5/2012 10:43:20 AM - arnie (192.168.1.102)> 257 "/" is current directory.
(001041)11/5/2012 10:43:20 AM - arnie (192.168.1.102)> TYPE I
(001041)11/5/2012 10:43:20 AM - arnie (192.168.1.102)> 200 Type set to I
(001041)11/5/2012 10:43:20 AM - arnie (192.168.1.102)> PASV
(001041)11/5/2012 10:43:20 AM - arnie (192.168.1.102)> 421 Could not create socket.
(001041)11/5/2012 10:43:20 AM - arnie (192.168.1.102)> disconnected.

[boco]

The Passive settings are wrong. FTP doesn't work with one port only! Port 21 is usually the listening port where the server receives the initial connections. It cannot be used as data port because it is already occupied. The custom port range, as the name says, must be a port range and should be at least 100 ports wide (to narrow down the possibility of running out of ports due to TCP time limits). The listening port plus the data range must be open in the firewall and forwarded in the router.

[benniegibson]

Thanks - I experimented and moved my ports for passive mode up to a higher range and have it working.
Appreciate the reply.