Cannot Connect WPF/WinForms Viewer to Report Server/REST Service

Environment

Product	Progress® Telerik® Reporting
Project Type	WPF and WinForms applications
Viewer	WPF/WinForms Report Viewer

Description

On attempt to connect WPF or WinForms ReportViewer to an engine of remote type, i.e. Report Server or REST Service, the following error occurs:

The assembly Telerik.Reporting.Services.HttpClient.dll cannot be loaded.

Solution

The Telerik.Reporting.Services.HttpClient.dll is required if the selected engine is of remote type (REST Service or Report Server). Please make sure that you have added a reference to this assembly to the current project.

It could be found in Telerik Reporting installation directory. For example C:\Program Files (x86)\Progress\Telerik Reporting 2025 Q1\Bin\Telerik.Reporting.Services.HttpClient.dll.

As a side note, we strongly suggest using the Telerik Report Viewer Window Item Template to create a window and host the report viewer in it. It will automatically add all required references and verify if all resources needed are added to the project.