During rig Move/up activities, one of the tasks was to spot the (BOP HPU: Hydraulic Power Unit) next to the subbase. This requires loading it from its position near runoff area and placing it on Oil field truck, then offload the same on the target spot near subbase. When the loading started and at around a height of 1m above the ground, the load became unbalanced causing one of the sling to slip from the skid trunnion (lifting points ).The HPU unit then flipped 90 degrees to the side due the sudden unbalance at such height on both cranes . No one was injured.