Can't transfer data over FTP

[thedust2010]

When trying to FTP files, the files and folders are being created, but no content for the files are uploaded. Instead all of the files have a filesize of 0 and I get the following error:

[11:40:25] PASV
[11:40:25] 227 Entering Passive Mode (129,41,59,85,5,203).
[11:40:25] PORT 129,41,59,85,5,203
[11:40:25] 200 PORT command successful
[11:40:25] RETR cmbs.php
[11:40:25] STOR cmbs.php
[11:40:37] 425 Can't open data connection.

Any ideas what is happening here?

NOTE: Using CentOS 4.3 and proftpd. The only firewall being used is IPTables.