The Report Viewer Web Control HTTP Handler has not been registered in the application's web.config file. Add <add verb="*" path="Reserved.ReportViewerWebControl.axd" type = "Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=15.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91" /> to the system.web/httpHandlers section of the web.config file, or add <add name="ReportViewerWebControlHandler" preCondition="integratedMode" verb="*" path="Reserved.ReportViewerWebControl.axd" type="Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=15.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91" /> to the system.webServer/handlers section for Internet Information Services 7 or later.
Report Viewer requires a standards compliant browser. Users of Internet Explorer 8 and earlier should switch to a modern browser, or if already using a modern browser target standards mode by adding the <meta http-equiv="X-UA-Compatible" content="IE=edge" > header tag to the host page.