Intuit has just implemented a new category feature for QuickBooks Online Products and Services lists. Only new QuickBooks Online company files (since I think November 2015) and selected existing ones have this new feature in it, they are slowly rolling it out to existing customers.
It is a big change which has an impact on Axis - we are in the process of updating Zed Axis to accommodate both the old sub items type structure and the new categories. That will be available in Axis v12 which we are working on right now.
In the meantime any products or services that are part of a category will encounter this error - a workaround is to not use the category feature for the moment until the update is here. We hope to have that in a a few weeks.