When releasing the Sales Order in Sales Company, and you get the followings error message:
This is most possible due to the fact, that the Supply Company, does not handle the Intercompany Inbox automatically, but manually.
As the Sales Order is not yet created in the Supply Company, it can't return a document no. and therefore no synchronization is made. But the order has been sent the Supply Company, and the order in the Sales Company will be updated with the document no. as soon as the Sales Order has been created in the Supply Company.