DMT Object reference not set to an instance of an object

Im getting this error when trying to import sales order combined Object reference not set to an instance of an object.

It creates the header fine but not the detail however when I split it and add the detail seperate it works fine, my ideal situation is to use the combined option so i dont have to loop back to get the sales order no

Assuming you actually have an order# of zero? OrderNum fields throughout the database have a default value of 0 rather than null to indicate there is no order number. OrderHed.OrderNum, being a primary key, can’t contain null. It seems they may have missed adding a constraint to prevent 0 existing as an OrderNum at the database.