This is a legacy report viewer and for new projects our recommendation is to use the latest web forms report viewer - HTML5 Web Forms Report Viewer
This article describes how to deploy Web Sites that use Telerik Reporting on a production server.
During the installation of Telerik Reporting on your machine, the Telerik assemblies were added to GAC. When deploying a Web Site project the assemblies from the GAC are not copied automatically so you need to make sure the assemblies physically exist in the bin folder of your application.
These assemblies add up to the core reporting functionality and should be used only if you need the specific feature. They are responsible for additional support formats, database session, retrieving data from an OLAP cube or using the Silverlight report viewer.
XPS rendering extension requires Telerik.Reporting.XpsRendering assembly (Telerik.Reporting.XpsRendering.dll).
The Telerik Reporting WCF Service (if needed) requires Telerik.Reporting.Service assembly (Telerik.Reporting.Service.dll).
Database Cache Provider requires Telerik.Reporting.Cache.Database.dll and Telerik Data Access.