Feb 09, 2016 09:02 AM|Will shao - MSFT|LINK
Seems that it is due to the httphandler changed.
Base on my experience, Reserved.ReportViewerWebControl.axd httpHandler is added to System.Web section of the Web.Config file. But it should be added to System.WebServer section.
I recommend you can see this similar thread:
Please add "Reserved.ReportViewerWebControl.axd" into you IIS server Handler Mappings .
Any concerns, please feel free to let me know.