Sorry, don't understand your question, it is not very clear.
The content page, must be placed in a ContentPlaceHolder within master page. Check you have setup your content placeholder and content pages correctly, with properly referenced master page. Check the Page Directives at the top of the content page. See the text below as examples of the Basics for Each Master and Content Page;
Master Page Basic Source;
<%@ Master Language="VB" CodeFile="MasterPage.master.vb" Inherits="MasterPage" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<asp:ContentPlaceHolder id="head" runat="server">
</head>
<body>
<form id="form1" runat="server">
The Master Page Button;<asp:Button ID="Button1" runat="server" Text="Button" />
</form>
<div>
the content place holder;
<asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">
</div>
</body>
</html>
Content Page Source;
<%@ Page Title="" Language="VB" MasterPageFile="~/MasterPage.master" AutoEventWireup="false" CodeFile="Default2.aspx.vb" Inherits="Default2" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">