SiteMap Object reference not set to an instance of an object

 Here's my web.sitemap file:

1
2 <siteMap xmlns="http://schemas.microsoft.com/AspNet/SiteMap-File-1.0" >
3 <siteMapNode url="~" title="Home" description="Test Site" roles="*">
4 <siteMapNode url="~/aboutUs.aspx" title="About Us" description="About Us" />
5 ...