Problem accessing through FTP Client

There are times when you come across an error message when you use FTP Client, the error message with be something like Failed to list directory or something like that. During such error make sure your Linux server has port 20 and 21 opened in IPTABLES. If those ports are allowed in your IPTABLES than make sure "ip_conntrack_ftp" module is loaded. Check in /etc/sysconfig/iptables-config if the following line exist:
IPTABLES_MODULES="ip_conntrack_ftp"

If it doesn't contain then add it or load it in module of kernal.

Loading module for Kernal using rc.local file.

# File: /etc/rc.local

# Module to track the state of connections
modprobe ip_conntrack

# Load the iptables active FTP module, requires ip_conntrack
modprobe ip_conntrack_ftp

# Load iptables NAT module when required
modprobe iptable_nat

# Module required for active an FTP server using NAT
modprobe ip_nat_ftp