Generally, this error occurs because the product that was originally synced to the accounting system is deleted. This results into Shypyard not being able to reference the product with the ID that was stored in the database.
Try out the following solution:
First, select the order with this error.
Click the drop-down option beside "Sync to Myob" and select "Re-Sync".
If this solution did not help resolve your error, please don't hesitate to reach out to us at [email protected] and we will look into resolving the issue for you.