"The Redhat IPtables startup script /etc/rc.d/init.d/iptables was not found on your system."
Starting with Fedora 16, iptables no longer has a startup script in init.d. It's been migrated to the systemd framework. Unfortunately, firewall/redhat-linux-lib.pl still looks for it.
Thanks - this will be fixed in the next Webmin release.
Webmin devel version 1.564 now includes Fedora 16 and systemd support.
yum install iptables-services