Hmmm ettercap should forward the data. Try using -u (think it was a little "u") to turn off ip_forward from ettercap and do it like this.
ettercap -T -u -q -i wlan0 -M arp /victum ip/ //
echo "1" > /proc/sys/net/ipv4/ip_forward
remember the -i wlan0 is MY interphase. You might have another.
Means just that. This does not look good. Could be a million reasons for this. Are you to far from the target. I am guessing you are not using BT4 since you have a working GTK. Is it set up right? In GTK under mitm try the one way poison.chkpoison reveals however that poisoning has not occured,