I have to admit the same. I ran about for a good 3 or 4 minutes trying to see where to put the C4. The problem is three fold (1) the mission brief says the BH is in two parts, so I was trying to C4 the rotor blades that were outside the barn. (2) The green marker for that objective location is outside the barn, and the BH body is inside the barn, I know it's big, but what can I say, I was under fire. And (3) You get a message about needing more C4, which is a confusing message because the C4 is already in your kit by default.
LMAO!