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Hi Hunty,
Thanks for posting on our forum.
I could understand your feeling. I know the issue caused some question for you.
According to the error message, the question is more related to custom code.
Since our forum is focus on SharePoint online, I’ll suggest you post a new thread in our MSDN forum for proper assistance.
To better help you, I have searched the error message for you on network, some users provide some suggestion for the same issue with you, you can refer to them:
Get Error 401 when trying to download a document from a library programatically
"The remote server returned an error: (401) Unauthorized"
Thanks for your understanding.
Qing