You forgot of starting your firewall rule with the word iptables. Try with the following piece of code:
if [ “$CHAIN” = FORWARD ] ; then
: # put here the commands for the chain FORWARD
iptables -A FORWARD -d 192.168.14.5 -i ETH00 -p tcp -m tcp –dport 21 –tcp-flags SYN,RST,ACK SYN -j ACCEPT
You should test it before rebooting by clicking the [Test] button. Do not forget to enable the Firewall script by using the [Enabled] flag.