This article explains the manual changes required when upgrading to Telerik Reporting Q3 2015 (188.8.131.520).
The viewer is build with Telerik UI Controls for WPF 2015.3.930.40. If you are using a newer version consider adding binding redirects. For more information see: How to: Add report viewer to a WPF application
The viewer is build with Telerik UI Controls for Silverlight 2015.3.930.1050.
TRDX files created by the Standalone Report Designer contain XML version http://schemas.telerik.com/reporting/2012/3.8