PASV port is same as FTP Server

From BulletProof Wiki

If your Passive port range is set to the same port that the FTP server is running on, the PASV mode tries to connect at the port that the FTP server is running on, so the server responds with the welcome message (220) (the server at this point thinks that someone is logging onto the server) However, you will see a few types of errors:

• You will see this error in your log file: "<- Unknown list format."
• In your client server side window, you will not see any folders. Instead you will only see "220" or something similar.
• Your server will freeze when an FTP client tries to use Passive mode.

To solve this problem, make sure that the FTP server port and the Passive port range are different.

Check the following BPFTP Server setting (most people use port 21):

• Setup --> Main --> General --> Connection --> Listen on Port number

Please also verify that the following port range does not include the port you are using above (i.e. don't use 21 if you used it above, the default range is 1024 - 65535):

• Setup --> Main --> Multi IP Settings --> Passive Mode --> Passive Port

If your router/firewall cannot forward enough ports to avoid this problem then many people will have problems using your server.