According to the bugtracker, this mission turns out to be as glitchy as hell, and if that alone was not enough, it also has its debriefing texts messed up, so “You did not follow your orders†may actually mean anything else.Regarding this particular issue, developers disclosed that there is a hidden timer set on 360 seconds that limits the execution of “Secure enemy position†task, which does not stop after the tank is destroyed. Moreover, I am afraid it starts when you first see the tank — not when you blow it. So this appears to be another crazy mission design as in “Within reachâ€, when the game tells you to go stealth, but the time is so strict that even Rambo style will not guarantee you success; in the current mission, however, the game not only keeps you from knowing you are short on time when giving you orders, but also does not give you any hint on what was the reason to consider the mission failed. This looks even more absurd when all friendly troops and APCs gather on the objective and pretty well satisfy for a “Seized by†trigger, but there is still an enemy soldier hiding behind distant buildings. So, despite developers instruct to disable all mods, I was able to complete the mission only with the help of “Support Call†addon by detecting each enemy's position.
As for other glitches during earlier parts of the mission, “You did not follow your orders†is usually triggered by going too far away from your team leader — not concisely, of course, but because either his car or yours stucks in rocks or vegetation, or because he chooses wrong path along obstacles in cemetery. Developers swear they fixed it (and then yet another time on each new ticket), but for vanilla AI only, — any AI-alterming mod (like “bCombatâ€) should be disabled. Otherwise, the mantra is as always — update / restart / revert / etc — however, taking into account how many bugs are there in that mission, I would not recommend to blindly restart the mission if you already made much progress, because chances are very high that you will face an impassable glitch in earlier tasks.
Curiously, after reading that the mission fails because the protagonist does not follow his leader, I spent much time trying to be as close as possible to him when he arrives at the objective that must be secured, which was difficult due to his marker “Follow†appears on map only and not on HUD even on easy settings. Meanwhile, the game was expecting me not sticking with the leader and keeping him secure, but to run in circles throughout the city eliminating each and any enemy soldier. Why making task description more specific was not an option for developers, is way beyond my understanding.