Over run after aborted takeoff. Some reports say landing short of the runway so some confusion - time will clarify.
Ancient Russian type operated in Africa by a "lowest bidder" freight charter operator - no surprises here. This sort of thing happens regularly in Africa where nobody learns from history.
Gross overloading and probable vodka involvement would by par for the course for these operations but we have no evidence yet so innocent until proven guilty. As usual we will probably never see a proper accident investigation report.