In Netsuite some users maintain multiple companies (subsidiaries). So they need to make sure that the items are enabled as active items for each company if they are going to use it under them. 

If you receive below error message when trying to import an order through TOE

[Code=INVALID_KEY_OR_REF] Invalid item reference key xxxx for subsidiary yy

That means the item xxxx is not enabled for the company yy. Ones that is done in the A/C system, when you right click the order and select Process in TOE the order should be imported

Go to Netsuite Setup --> Company --> Subsidiaries 

There you will see the Internal ID which is value yy

Now go to the item in Netsuite and make sure that particular subsidiary company is set up against that item.

Please contact TOE support (support@theorderexchange.com.au) if you have more issues.