You can use the following code:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
var instanceReportSource = new Telerik.Reporting.InstanceReportSource();
instanceReportSource.ReportDocument = new YourClassLibrary.YourReport();
this.ReportViewer1.ReportSource = instanceReportSource;
}
}
You can also set the ReportSource declaratively from the ReportViewer properties.