The active schema do not support the element

Question

Hello, I am quite new to .NET and C#, so I hope these questions are not too stupid. I`m a student trying to learn Visual Studio .NET, and right now we are working with developing mobile webpages. My problems is using templates inside a webform, I can`t work it out. If I for instance try some code some person have developed, I get some error messages. This is a code some programmer here at c-sharpcorner have developed, so I guess there is nothing wrong with the code; <%@ Page Inherits="System.Web.UI.MobileControls.MobilePage" %> <%@ Register TagPrefix="mobile" Namespace="System.Web.UI.MobileControls" Assembly="System.Web.Mobile" %> //This is where I get error message.... //This is where I get error message.... I then gets the message "The active schema do not support the element 'choice'", and the active schema do not support the element 'HeaderTemplate'". Am I doing someting wrong? Hoping for an answer:) Halvor Nordbø, Norway