Security Trimming Not Working Properly

I've implemented a menu via Web.sitemap, which I would like to respect the Role settings I've included in it.  I followed this article precisely but it doesn't work: http://msdn2.microsoft.com/en-us/library/ms178428(VS.80).aspx
Here's the pertinent section in my web.config file:
        <siteMap defaultProvider="XmlSiteMapProvider" enabled="true">
            <providers>
                <add name="XmlSiteMapProvider" description="Default SiteMap provider." type="System.Web.XmlSiteMapProvider" siteMapFile="Web.sitemap" securityTrimmingEnabled="true"/>
            </providers>
        </siteMap>

 
In my cu ...