Alright i'm trying to follow this treeview tutorial, and I get:

Parser Error Message: File or assembly name Microsoft.Web.UI.WebControls, or one of its dependencies, was not found.
For:

<%@ Register TagPrefix="mytree" Namespace="Microsoft.Web.UI.WebControls" Assembly="Microsoft.Web.UI.WebControls, Version=1.0.2.116, Culture=neutral, PublicKeyToken=31bf3856ad364e35" %>
Microsoft .NET Framework Version:1.0.3705.209; ASP.NET Version:1.0.3705.0

I've installed the IE Web Controls as the article said.