Problem 1 : This page is missing a HtmlHead control which is required for the CSS stylesheet link that is being added. Please add <head runat=”server” />

Solution :  make your HEAD tag  to <HEAD runat=”server”>

problem 2 : The Controls collection cannot be modified because the control contains code blocks (i.e. <% … %>).

Solution:  Looks like you are using <% tags in your HEAD section code like Javascript code etc…. To fix it wrap your head section with <div runat=”server”>  and </div>