The error you see means that the user you use does not have view permissions for pages( or for a page). The 403 status is currently not handled and this is something that we are going to worn next Q. By default the ASP.NET SiteMapProvider also does not return information whether the page is not accessible or it is not presented in the current sitemap. Since we follow the default implementation of ASP.NET SiteMapProvider we are also affected from this issue and we are working on a solution about it. The problem is in the request - once a user that is not authenticated
tries to access a page he/she will get 404 error instead of going to the login page.
the Telerik team