From terminal, execute the following;
sudo modprobe ip_nat_ftp ports=21
sudo modprobe ip_conntrack_ftp
sudo iptables -A FORWARD -m state --state ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -p tcp -m tcp -m state --dport 21 --state NEW -j ACCEPT
sudo iptables -A FORWARD -p tcp -m tcp -m state --sport 20 --state RELATED -j ACCEPT
sudo iptables -A FORWARD -p tcp -m tcp -m state --dport 1024:65535 --sport 1024:65535 --state RELATED -j ACCEPT
