Ettercap causes IP conflicts

Hello all
I am using Backtrack4 in VM and wanted to play around with IronGeeks old 'Fun with Ettercap' filter. I have followed his tutorial but when I launch

ettercap -T -q -F ig.ef -M ARP /Target/ //

it causes IP conflicks.

I have not edited the etter.conf. Not sure if it needs it.

I have also ran in another shell

echo 1 > /proc/sys/net/ipv4/ip_forward

any ideas why this would be happening?

I thing you may be getting this because ettercap is telling target_ip that it is target_ip as well. I'm not sure what the syntax might be to stop this.