The assembly Telerik.ReportViewer.Wpf.Design.dll doesn't contain the required WPF assemblies as resources, which results in the following error when trying to add a viewer from the Visual Studio item template:
Error: Can not resolve assembly from Telerik.ReportViewer.Wpf.Design.Resources.Telerik.Windows.Data.dll
Error: System.ArgumentException: The path is not of a legal form.at System.IO.Path.NewNormalizePath(String path, Int32 maxPathLength, Boolean expandShortPaths)at System.IO.Path.NormalizePath(String path, Boolean fullCheck, Int32 maxPathLength, Boolean expandShortPaths)at System.IO.Path.GetFullPathInternal(String path)at System.Reflection.AssemblyName.GetAssemblyName(String assemblyFile)at Telerik.ReportViewer.Wpf.Design.Resources.GetResourceAssemblyName(ITracer tracer, String asmName)
Error: System.NullReferenceException: Object reference not set to an instance of an object.at Telerik.ReportViewer.Wpf.Design.ItemTemplateWizard.CheckTelerikWpfReferences()at Telerik.ReportViewer.Wpf.Design.ItemTemplateWizard.RunStartedCore(Dictionary`2 replacementsDictionary)