First Propaganda mision will not complete
Solution 1:
Just like everything else in the game, fry cry highlights everything that's objective related.
There is a red meter on the top of your screen that shows your progress. Go through each room and take out all computers, stamping machines, boxes of posters, Transportation vehicles, and most importantly the power generator.
Power generators needs to be taken out using C4 or explosives of some kind. After all this is finished, you'll get a few more waves of men, take them out. And that should complete the mission.
Solution 2:
You have to destroy all propaganda material and kill all enemies surrounding the area. Maybe if you do mission like I did - use the Buzzer and grenade launcher to destroy the propaganda and kill all targets - it will work.
Solution 3:
Sometimes the pick-up trucks fail to count as 'destroyed' even when they've been blown up. If they're still 'flashing' and a handful of C4 doesn't change this, then you sadly have to restart the mission.