The Report Viewer Web Control HTTP Handler has not been registered in the application's web.config file

Question

    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=9.0.0.0, 
Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" /> to the system.web/httpHandlers section of the web.config file

This error is coming . I have already mentioned this line in http handler but still getting this error

<add path="Reserved.ReportViewerWebControl.axd" verb="*"   type="Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=8.0.0.0,    Culture=neutral, PublicKeyToken=0000000000000000" validate="false" />

my html page markup is as follow

<%@ Register Assembly="Microsoft.ReportViewer.WebForms, Version=9.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
    Namespace="Microsoft.Reporting.WebForms" TagPrefix="rsweb" %>

<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<asp:Button ID="btnsubmit" runat="server" OnClick="GenerateReportButton_Click" />
    <rsweb:ReportViewer ID="ReportViewer1" runat="server">
    </rsweb:ReportViewer>
</asp:Content>

Web config assemblies section is as follows :

<assemblies>
    <add assembly="System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
    <add assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
    <add assembly="System.Data.DataSetExtensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
    <add assembly="System.Xml.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
    <add assembly="System.Web.DataVisualization, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
    <add assembly="System.Windows.Forms, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
    <add assembly="Microsoft.ReportViewer.WebForms, Version=9.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
    <add assembly="Microsoft.ReportViewer.Common, Version=9.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
</assemblies>

Answer 1

I was having the very same problem. What happened was I put the Report loading routine on Page_Load, and didn't wrap it in if (!IsPostBack). The ReportViewer makes a POST to the page, and that was triggering Page_Load and reloading the report, somehow messing it up. After putting everything inside if (!IsPostBack), it worked like a charm.