This article explains the manual changes required when upgrading to Telerik Reporting Q3 2015 SP1 (220.127.116.115).
The viewer is build with Telerik UI Controls for WPF 2015.3.1104.40. If you are using a newer version consider adding binding redirects. For more information see: How to Add report viewer to a WPF .NET Framework project
The viewer is build with Telerik UI Controls for Silverlight 2015.3.1104.1050.
The default report viewer template now uses a Telerik proprietary font. The font is located in C:\Program Files (x86)\Telerik\Reporting R2 2020\Html5\ReportViewer\font. The font folder and its content should be present in the ReportViewer folder of your report viewer application.
The property Parameters is now read-only, allowing the containing parameter instances to be accessed by name.