The Australian Army must have thought their Hamel guns were cursed at one stage some years ago regarding Blackhawk moves -
one was dropped in transit (crew swore blind they didn't do it inadvertantly, and the systems checked out fine so it was in the unexplained basket) (lesson - weird **** can sometimes happen so don't fly over anything you don't want to bomb);
then another was being picked up at night on goggles and one of the strops caught around part of the gun causing it to swing unstably to such an extent the helicopter crew thought it would hit the main rotor, so they pickled it (lesson - make sure the rigging is all hanging right before going too far from where you picked up the load);
then (non helicopter related), a gun crew were manhandling one around when it charged off down a hill and destroyed itself (lesson - grunts often break things).
There was also the RAAF Iroquois crew who spotted a beached dinghy washed up somewhere along our extensive northern coastline and decided to salvage it. Cobbled up some ropes and strops and hung it off the hook, off they went happily until some airspeed was gained and the boat started to fly dangerously, some ropes broke, dinghy was pickled. (lesson - use the right gear and be careful of how stuff flies).
Then there was the Aussie pilot on a brief exchange trip with some US Iroquois guys in the middle east. Aussie way was to note temperature and PA and work out the lifting capability of the aircraft for each load, but apparently the yanks at this unit would work it out in the morning on expected conditions. The helicopter took off with the Aussie as copilot to lift a water bladder up to a higher elevation hilltop OP, approaching the drop point and slowing down it becomes apparent that the power available is less than that required, load starts to scrape along the ground and threatens to drag the helicopter in with it, copilot pickles the load. (lesson - note the actual conditions and figure out your lifting capability based on them).
That reminds me of the Aussie Iroquois that put down with a chip light or similar somewhere in the bush, needed to be external loaded home by Chinook. The Chinook lifts it out at warp factor five and in so doing causes a lot more damage to the poor old Huey than was originally the case. (lesson - rig carefully and go gently).