The court of arbitration for sport has found in favour of the original decision made by the ground judges and then the F.E.I Appeal Committee.
The Irish team appealed the result after a steward had ran on the course while O'Connor was competing in his final round at the event in Achen last August
The Meath man had been on course for a clear round before a member of the ground crew member ran in front of him and had to jump into a flower bed to get out of the way.
O'Connor was the only rider to knock the next fence, leaving Ireland just 0.38 penalties behind Spain, who earned the last Olympic place.
