When transferring files to or from your ftp server you will need to have passive ports defined in pure-ftpd and allowed in the firewall.
These are often not defined correctly by pure-ftpd or your firewall, even though you may be using CWP.

First define the Passive Port Range in the pure-ftpd config file

nano /etc/pure-ftpd/pure-ftpd.conf

 Uncomment (remove # at beginning of the line) PassivePortRange and specify the passive port range:

PassivePortRange 30000 50000

 * If this line is missing then simply add it at the end of the file.

Restart pure-ftpd to load the new configuration

service pure-ftpd restart

 Then define the port range in the CSF firewall configuration (if you're using CWP)
In the file /etc/csf/csf.conf add the same port range under TCP_IN and TCP_OUT

nano /etc/csf/csf.conf

In lines TCP_IN and TCP_OUT add 30000:50000, example

# Allow incoming TCP ports
TCP_IN = "20,21,22,25,53,80,110,143,443,465,587,993,995,2030,2031,30000:50000,6666"

# Allow outgoing TCP ports
TCP_OUT = "20,21,22,25,53,80,110,113,443,2030,2031,30000:50000,993,995"

 Finally reload csf firewall configuration

csf -r