Counter Attack never seems to have worked properly for me. I am attacked by much higher level Vikings but when I try to set defensive Counter Attacks it will not let me. I have sufficient gold, stamina and have been attacked within the last 24 hours but it will not let be set a counter attack. I would understand if it never worked but it does from time to time. Just seems absolutely random.
You may have hit the limit of how many you can set, as a low level you can set more as you go higher the amount is less, if I am not mistaken it drops to 10 counters. See if it is telling you that you reached the limit, it should if you have it would say this: Please reduce the number of counter attacks in order to setup a new one. Click here to visit the counter attack and bounty trap page.