Adding HtmlAgilityPackSanitizerProvider

I am having trouble with adding the required text to the web.config file for the HtmlAgilityPackSanitizerProvider.

Even when I open the sample site from the toolkit in Visual Web Developer I get an error.
The element 'system.web' has an invalid child element 'sanitizer'.
Not sure how to get this to work. 

This is the section of the toolkit sample site:
<configuration>
<configSections>
<sectionGroup name="system.web">
<section name="sanitizer" requirePermission="false"
type="AjaxControlToolkit.Sanitizer.ProviderSanitizerSection, AjaxControlToolkit" />
</sectionGroup>
</configSections>
<appSettings/>
<connectionStrings/>
<system.web>
<trust level="Full" />
<sanitizer defaultProvider="HtmlAgilityPackSanitizerProvider">
<providers>
<add name="HtmlAgilityPackSanitizerProvider" type="AjaxControlToolkit.Sanitizer.HtmlAgilityPackSanitizerProvider"></add>
</providers>
</sanitizer>