Ok, I'm still a little confused. I set my planet as the source and his as the destination. Once the harvester got to his planet nothing happened. However, while my harvester was still in his orbit, I clicked on my unit and a new icon was available. It was next to the harvest resource button and had two larger arrows - It was the trade button. I clicked the button and then it asked for a destination. Since I was already at his I picked his planet. Nothing happened, so I tried again, this time I picked my planet using the new trade button and my ship jumped and started making its way back to my colony. It is now on its way back to my trade partner's planet (On an Auto Route). There is no notification telling you how much ore was gained in the transaction though... Anywhere we can find that?