can't detonate c4

[PostFatal]

I'm trying to play through the single player mode of Sniper Ghost warrior and I am at the part where I have to blow up AA guns with c4. I have collected the c4 and it says to use left mouse button to throw the c4 and then it says %(_ACTION_FIRE_RHAND_WEAPON to detonate. I assume this is right mouse button but it doesn't work. I've looked through the key bindings but don't find it. Any help would be much appreciated. Thanks.