Clean install, no errors, totally successful, added no modules, no child portals. Changed skin from default DNN blue to the DNN grey skin on the default portal as superuser, and now the site is totally inaccessible:

An error has occurred.
DotNetNuke.Services.Exceptions.PageLoadException: Value cannot be null. Parameter name: type ---> System.ArgumentNullException: Value cannot be null. Parameter name: type at System.Activator.CreateInstance(Type type, Boolean nonPublic) at DotNetNuke.Framework.Reflection.CreateObject(String TypeName, String CacheKey, Boolean UseCache) at DotNetNuke.Framework.Reflection.CreateObject(String ObjectProviderType, String ObjectProviderName, String ObjectNamespace, String ObjectAssemblyName, Boolean UseCache) at DotNetNuke.Modules.NavigationProvider.NavigationProvider.Instance(String FriendlyName) at DotNetNuke.UI.Skins.NavObjectBase.InitializeNavControl(Control objParent, String strDefaultProvider) at DotNetNuke.UI.Skins.Controls.TreeViewMenu.OnInit(EventArgs e) at System.Web.UI.Control.InitRecursive(Control namingContainer) at System.Web.UI.Control.InitRecursive(Control namingContainer) at System.Web.UI.Control.InitRecursive(Control namingContainer) at System.Web.UI.Control.AddedControl(Control control, Int32 index) at System.Web.UI.ControlCollection.Add(Control child) at DotNetNuke.Framework.DefaultPage.Page_Init(Object sender, EventArgs e) at System.Web.UI.Control.OnInit(EventArgs e) at System.Web.UI.Page.OnInit(EventArgs e) at DotNetNuke.Framework.PageBase.OnInit(EventArgs e) at System.Web.UI.Control.InitRecursive(Control namingContainer) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---

download a different package, say the upgrade version, and find in the bin/ directory some dlls that were not included in the install and (I believe I have read) starter versions.

One of these dll files is DotNetNuke.DNNTreeNavigationProvider.dll. Upload this to the bin/ directory of your installation, and then test vertical menu on a test page.

There are a few threads that list a handful of other dll files that also did not get into the install package, with some justification it seems as they aren't all necessary. However, I think the above dll file was not included by mistake as vertical menus are necessary to support.

There are some other alternate menu providers among the missing dlls. I have not tested to see, but I think it is just this one that is required for vertical menus.