Hi There,
Have you tried making the Customer Active in QuickBooks? you can do this by navigating to the Customers App in QBO, and clicking on the Gear Icon in the top right hand corner of the Customer Grid. In the dropdown that appears, you will have the option of displaying Inactive customers as well.
Here is a screenshot of what im talking about;
http://i.imgur.com/ICm7Pyj.png
Let me know how you go.
Thanks!
Regards,
Ben