Report Viewer Configuration Error, error message hidden in HML using ASP.NET report viewier control

I have an ASP.NET web form that uses a report viewer control, which generates the messagehidden (display:none) in HTML, below:

<span id="ReportViewer1_ReportViewer"><div id="ReportViewer1" InteractiveDeviceInfos="(Collection)" onclick="if ($get(&#39;ReportViewer1_ctl04&#39;) != null &amp;&amp; $get(&#39;ReportViewer1_ctl04&#39;).control != null) $get(&#39;ReportViewer1_ctl04&#39;).control.HideActiveDropDown();" onactivate="if ($get(&#39;ReportViewer1_ctl04&#39;) != null &amp;&amp; $get(&#39;ReportViewer1_ctl04&#39;).control != null) $get(&#39;ReportViewer1_ctl04&#39;).control.HideActiveDropDown();" style="height:400px;width:400px;"><div id="ReportViewer1_HttpHandlerMissingErrorMessage" style="border-color:Red;border-width:2px;border-style:Solid;padding:10px;display:none;overflow:auto;font-size:.85em;"><h2>
			Report Viewer Configuration Error</h2><p>The Report Viewer Web Control HTTP Handler has not been registered in the application&#39;s web.config file.  Add &lt;add verb=&quot;*&quot; path=&quot;Reserved.ReportViewerWebControl.axd&quot; type = &quot;Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a&quot; /&gt; to the system.web/httpHandlers section of the web.config file, or add &lt;add name=&quot;ReportViewerWebControlHandler&quot; preCondition=&quot;integratedMode&quot; verb=&quot;*&quot; path=&quot;Reserved.ReportViewerWebControl.axd&quot; type=&quot;Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a&quot; /&gt; to the system.webServer/handlers section for Internet Information Services 7 or later.</p><
/div>

Which renders like below (please note that it is originally hidden in HTML (display:none)):

Report Viewer Configuration Error

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=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" /> 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=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" /> to the system.webServer/handlers section for Internet Information Services 7 or later.

The webconfig has already used below:

<configuration>  <appSettings>    <add key="ReportViewerServerConnection" value="WebForm.Lab.ReportConnection, WebForm" />          </appSettings>  <system.web>    <httpHandlers>      <add path="Reserved.ReportViewerWebControl.axd" verb="*" type="Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" validate="false" />    </httpHandlers>  </system.web>  <system.webServer>    <handlers>      <add name="ReportViewerWebControlHandler" preCondition="integratedMode" verb="*" path="Reserved.ReportViewerWebControl.axd" type="Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />    </handlers>  </system.webServer></configuration>

Is this by design or an error? How to fix it if it is an error