@woodymoo I have tried this tutorial and adding the source as URL and file worked in my case.
In your case I think there is some issue with the search service linked to your question answering resource that is causing this to fail. You can try to sync the search service with your question answering resource from azure portal.
Ensure to delete the sources from the language studio before trying to re-sync.
If the above steps do not work you can try to re-create the resources and check if it is successful.
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