What about selinux? Is selinux enabled? If not then you can give following command a try:
insmod /lib/modules/`uname -r`/kernel/net/netfilter/nf_conntrack_ftp.ko
Once done try to FTP and run ls command and it should show you the listing.
If the command works then you can put this entry in /etc/rc.d/rc.local to make sure that system load this module everytime after reboot.