iptalbes tool relies on a kernel module interacting with netfilter to control network traffic.
This error happens while iptalbes cannot found that module in kernel, so iptables suggest you to upgrade it :)
Perhaps iptables or your kernel needs to be upgraded.
However in most cases it's just the module not added to kernel or being banned, try this command to check whether be banned:
cd /etc/modprobe.d/ && grep -nr iptable_nat
if the command shows any rule matched, such as blacklist iptable_nat or install iptable_nat /bin/true, delete it. Since iptalbes will cost some performance, it's not strange to ban it while not necessary.
If nothing found in blacklist, try add iptable-nat to the kernal manual:
modprobe iptable-nat
If all of above not works, you can consider really upgrade your kernal...