title: MvcSiteMapProvider and web.config: Parser Error Message: Value cannot be null
body: <p>In my web.config file I have:</p>
  
  <pre><code>&lt;siteMap defaultProvider="MvcSiteMapProvider" enabled="true"&gt;
        &lt;providers&gt;
          &lt;clear /&gt;
          &lt;add name="MvcSiteMapProvider"
               type="MvcSiteMapProvider.DefaultSiteMapProvider, MvcSiteMapProvider"
               siteMapFile="~/Mvc.Sitemap"
               securityTrimmingEnabled="true"
               cacheDuration="5"
               enableLocalization="false"
               scanAssembliesForSiteMapNodes="true"
               excludeAssembliesForScan=""
               includeAssembliesForScan=""
               attributesToIgnore=""
               nodeKeyGenerator="MvcSiteMapProvider.DefaultNodeKeyGenerator, MvcSiteMapProvider"
               controllerTypeResolver="MvcSiteMapProvider.DefaultControllerTypeResolver, MvcSiteMapProvider"
               actionMethodParameterResolver="MvcSiteMapProvider.DefaultActionMethodParameterResolver, MvcSiteMapProvider"
               aclModule="MvcSiteMapProvider.DefaultAclModule, MvcSiteMapProvider"
               siteMapNodeUrlResolver="MvcSiteMapProvider.DefaultSiteMapNodeUrlResolver, MvcSiteMapProvider"
               siteMapNodeVisibilityProvider="ekmProspector.web.SiteMapProviders.AuthenticatedVisibilityProvider, ekmProspector"
               siteMapProviderEventHandler="MvcSiteMapProvider.DefaultSiteMapProviderEventHandler, MvcSiteMapProvider"
           /&gt;
        &lt;/providers&gt;
      &lt;/siteMap&gt;
  </code></pre>
  
  <p>I also have project reference to the MvcSiteMap library dll, a sitemap named mvc.sitemap.
  The pages namespaces also look like:</p>
  
  <pre><code>   &lt;pages&gt;
        &lt;namespaces&gt;
          ...
          &lt;add namespace="MvcSiteMapProvider.Web.Html"/&gt;
          &lt;add namespace="MvcSiteMapProvider.Web.Html.Models"/&gt;        
        &lt;/namespaces&gt;
      &lt;/pages&gt;
  </code></pre>
  
  <p>However, whenever I browse to any page in my MVC3 project I get the following error:</p>
  
  <blockquote>
    <p>Configuration Error Description: An
    error occurred during the processing
    of a configuration file required to
    service this request. Please review
    the specific error details below and
    modify your configuration file
    appropriately.</p>
    
    <p>Parser Error Message: Value cannot be
    null. Parameter name: type</p>
  </blockquote>
  
  <p>And the source error is pointing to this line:</p>
  
  <pre><code>Line 91:         &lt;clear /&gt;
  Line 92:         &lt;add name="MvcSiteMapProvider"
  Line 93:              type="MvcSiteMapProvider.DefaultSiteMapProvider, MvcSiteMapProvider"
  </code></pre>
  
  <p>Why am I getting this error?</p>