MvcSiteMapProvider and web.config: Parser Error Message: Value cannot be null - asp.net-mvc-3

Question

In my web.config file I have:
<siteMap defaultProvider="MvcSiteMapProvider" enabled="true">
<providers>
<clear />
<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"
/>
</providers>
</siteMap>
I also have project reference to the MvcSiteMap library dll, a sitemap named mvc.sitemap.
The pages namespaces also look like:
<pages>
<namespaces>
...
<add namespace="MvcSiteMapProvider.Web.Html"/>
<add namespace="MvcSiteMapProvider.Web.Html.Models"/>
</namespaces>
</pages>
However, whenever I browse to any page in my MVC3 project I get the following error:
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.
Parser Error Message: Value cannot be
null. Parameter name: type
And the source error is pointing to this line:
Line 91: <clear />
Line 92: <add name="MvcSiteMapProvider"
Line 93: type="MvcSiteMapProvider.DefaultSiteMapProvider, MvcSiteMapProvider"
Why am I getting this error?

Answer 1

I eventually found out myself what the problem was. The MvcSiteMap provider library uses the reflection Activator.Createinstance() method to call into the provider you set-up in the sitemap file. If the format of the provider is incorrect, Activator fails with the above message.
For example, the value in the sitemap for a visibilityprovider should be "fullqualifiednamespace.ProviderClass, AssemblyName".
e.g. "MyApplicationNamespace.AuthenticationVisibilityProvider, MyApplication"