Try this
SELECT T.TCode, (Select distinct V.VehicleID from TblConfirmedVehicleMap V where V.ReplyID=T.ReplyID)
FROM TblTransactions T
WHERE T.LoadID=1
But I fear that there are repeating Reply IDs in either or both the tables. If so and you still want one of the Reply IDs to get selected then try this:
SELECT T.TCode, (Select V.VehicleID from TblConfirmedVehicleMap V where V.ReplyID=T.ReplyID and rownum = 1)
FROM TblTransactions T
WHERE T.LoadID=1
Hope it helps :)