Can't finish the forest level.

[Soul XCV]

When I hop on the back of the truck, it says objectives 3/4 and the level won't complete. I've killed every enemy on the map except for the last guy that's gonna fail the mission. What else should I do?

[medoed234]

most likely u didnt take the rifle spy, in the place where the soldier and the officer are talking(after the tunnel next to the tower, not far from the base), follow the officer, he goes straight to her

[Kritzburgh]

You probably got softlocked by killing the guard in the water tower on the side that's facing the last guard. This can cause that last guard by the truck to be in a permanent "alterted" state, but without him actually running and setting off the alarm to give the player a "Mission Failed" fail state. It sucks, and it's why the Forest level is infamous for being buggy and, quite frankly, garbage. You'll have to restart the level. Load up the forest autosave in your Load Game options under "Show Autosaves".

Like the other comment said, If you didn't find the Snooper Rifle (press N for notebook to check objectives), then that's another objective you have to complete.

[VVanTuz2OO2]

Originally posted by Soul XCV:

When I hop on the back of the truck, it says objectives 3/4 and the level won't complete. I've killed every enemy on the map except for the last guy that's gonna fail the mission. What else should I do?

I had that bug in the pirated version which made me buy it on Steam. Though, replay it. If you still cannot procced in the truck, press N, which is by default bringing you the Notebook containing all the brifieng stuff: instructions and tips, and list of tasks as well. The tasks you had completed are marked with V. So, I was able to almost complete the level without Snooper rifle, though it is a TASK to obtain it (which also means if you don't have one, you cannot end the mission), so I went back, and after obtaining it i have completed the mission. Why I am telling you that? Simply that book can tell you if you are not done.

That is also comes in handy later in the game, when tasks are not that much obvious.

[QWEEDDY2]

Question already answered, yes.

Just by the way info
You can kill everyone in this mission after you got inside. If you say true that you kill almost everyone - you already raech that part, when you can backtrack to kill everyone else.