I ran across this error when installing a new Release Agent and it got to the Azure File Copy stage. Many of the solutions on the Internet to this problem point to it being caused by incorrect times on the Agent machine or the target server. However all servers had the correct time and were in the same time zone.
My problem appeared to be caused by my token Endpoint from VSTS connecting me to Azure. When I renewed this endpoint certificate the Azure File Copy task magically worked. The only difference I could see from the previous agent I had, was that my new Agent was a new Virtual Machine compared to the older one which was a Classic Azure Virtual Machine.
I hope this helps someone.