I suspect then that you may have missed doing this part of the sample:
"When creating Aspx WebForms, the pages you create do by default inherit from System.Web.UI.Page. In order to have Visual WebGui specific attributes available within the WebForm, you need to change the inheritance so that your WebForm inherits from Gizmox.WebGUI.Forms.Hosts.AspPageBase."
you need to change the declaration of WebForm2 from this:
public partial class WebForm2 : System.Web.UI.Page
public partial class WebForm2 : Gizmox.WebGUI.Forms.Hosts.AspPageBase
PS the file does not physically exist - it is an embedded resource that is generated at IIS Runtime by the Gizmox dlls - which explains why you can't find it in Windows Explorer