[Badger(new)]

pawn Код:

forward RespawnEmptyCars();
public RespawnEmptyCars()
{
  for(new i; i<MAX_VEHICLES; i++)
  {
    if(!IsVehicleOccupied(i))
    {
      SetVehicleToRespawn(i);
    }
  }
  return 1;
}

You should return 1; at the end. Also, you don't need to state that "i=0" since it automatically is equal to 0 when you create it (new).