Hi, I don't know what that error means.
Use the scripts to check.
sudo iptables -t nat -A POSTROUTING -o eth2 -j MASQUERADE
Make sure you change "eth2" to suit the external network.
($IPTABLES -A POSTROUTING -t nat -o $EXT_IF
eg. on my system it is eth0. where, eth0=ext_if and eth1=int_if
That's all I got.