Why is my complete menu disappearing when Security Trimming is set to "True"

When I have security trimming set to "False" ~ my menu works fine, but whenever I set it to "True", the complete menu dissappears.

My Web config file is as follows ...

<siteMap defaultProvider="AspNetXmlSiteMapProvider" enabled="true">
      <providers>
        <remove name="AspNetXmlSiteMapProvider"/>
        <add name="AspNetXmlSiteMapProvider" description="Default SiteMap provider." type="System.Web.XmlSiteMapProvider" siteMapFile="Web.sitemap" securityTrimmingEnabled="true"/>
      </providers>
    </siteMap>

My Web SiteMap file is currently as follows (albeit this has been chopped and changed a bit as I have been trying different options) ...

<?xml version="1.0" encoding="utf-8" ?>
<siteMap enableLocalization="true" xmlns="http://schemas.microsoft.com/AspNet/SiteMap-File-1.0" >

    <siteMapNode>
        <siteMapNode roles="*" >
           
        </siteMapNode>
      
        <siteMapNode url="Default.aspx" title=" Home  | "  description="Home Page" roles="*" >
                          
           
            <siteMapNode url="" title="About Us" description="About Us" roles="*" />
            <siteMapNode url="Login.aspx" title="Login" description="LogIn page" roles="*" />

        </siteMapNode>
      
       
        <siteMapNode url="" title=" How it Works   |  " description="Site Operation" roles="*" >
            <siteMapNode url="" title=" Take a Tour " description="Link to Video" roles="*" />
           
        </siteMapNode>   
       
        <siteMapNode url="" title=" View  |  " description="View Menu" roles="*" >
            <siteMapNode url="~/Members/All_Locums.aspx" title="All Locums  "  description="View Locums in the System" roles="*" />
            <siteMapNode url="~/Members/All_Companies.aspx" title="All Companies" description="View All Companies in the System" roles="*" />
            <siteMapNode url="~/Members/All_Pharmacies.aspx" title="All Pharmacies" description="View All Pharmacies in the System" roles="*"/>
            <siteMapNode url="" title="Vacancies" description="View All Current Vacancies" roles="*" />
        </siteMapNode>
         
       
        <siteMapNode url="" title="Locums  |" description="Locum Pages" roles="Locum" >
            <siteMapNode url="~/Locums/Locumsonly.aspx" title="Locums Only" description="Restricted Page" roles="Locum" />
             <siteMapNode url="~/Locums/My_Profile.aspx" title="My Profile" description="View Your Profile" roles="Locum" />
                   
                <siteMapNode url="" title="Vacancies" description="View Vacancies" roles="Locum" >
                <siteMapNode url="" title="View All" description="All Vacancies" roles="Locum" />
                <siteMapNode url="" title="View Preferred" description="Preferred Vacancies" roles="Locum" />
              
            </siteMapNode>
        </siteMapNode>

               
        <siteMapNode url="" title=" FAQs  | "  description="FAQ" roles="*" />
        <siteMapNode url="~/Help.aspx" title=" Help  |"  description="Help" roles="*"  target="_blank"/>
        <siteMapNode url="" title=" Contact Us  | "  description="Contact Us" roles="*" />
       
        </siteMapNode>
       
           
    </siteMap>

Finally, I have Web.config files on each of the directories as follows ...

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <system.web>
        <authorization>
            <allow roles="Locum" />
            <deny users="?" />
            <deny users="*" />
        </authorization>
    </system.web>
</configuration>

There is obviously something I am missing.   Any help would be appreciated.  It's driving me mad !!!!

Ta

Stuart