Register Ajax tookit

Hi,

I have installed the Ajax toolkit and also registered it in the web config file (attached). However, when I try to use one of its components (like ToolkitScriptManager and CalendarExtender), I get an error that it is not a known element.

Could anyone pls tell what else I need to do in order to use the Ajax components ?

Thanks.

<?xml version="1.0" encoding="utf-8"?><configuration><appSettings /><connectionStrings><add name="ConnectionString" connectionString="Data Source=server;Initial Catalog=sample;Integrated Security=True" providerName="sample.Data.SqlClient" /></connectionStrings><system.web><customErrors mode="Off" /><compilation debug="true" targetFramework="4.0" /><!--
            The <authentication> section enables configuration
            of the security authentication mode used by
            ASP.NET to identify an incoming user.
        --><authentication mode="Windows" /><!--
            The <customErrors> section enables configuration
            of what to do if/when an unhandled error occurs
            during the execution of a request. Specifically,
            it enables developers to configure html error pages
            to be displayed in place of a error stack trace.<customErrors mode="RemoteOnly" defaultRedirect="GenericErrorPage.htm"><error statusCode="403" redirect="NoAccess.htm" /><error statusCode="404" redirect="FileNotFound.htm" /></customErrors>
        --><pages controlRenderingCompatibilityVersion="3.5" clientIDMode="AutoID"><controls><add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" /></controls></pages></system.web><!--
        The system.webServer section is required for running ASP.NET AJAX under Internet
        Information Services 7.0.  It is not necessary for previous version of IIS.
    --></configuration>