Causes:
You have content in the same way like the old .aspx file including tags. However, when you use a master page, all content on all other pages should go into tag.

Solution:
Example,

%@Page Language=”VB” AutoEventWireup=”False” CodeFile=”Login.aspx.vb” Inherits=”Login” MasterPageFile=”Masterpage.master”%

<asp:content id=”content” contentplaceholderid=”contentplaceholder1″ runat=”server”>

content goes here!

</asp:content>

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Exception : System.Web.Exception 1

Content controls are only allowed in content page that references a master page.

Causes : Missing MasterPageFile=”Masterpage.master” attribute in current file.

Solution  : Add it.

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