Master Page Weirdness - "Content controls have to be top-level controls in a content page or a nested master page that references a master page."

This is weird. I added a brand new Web Application project to my solution in Visual Studio 2008.

Created a master page. Made zero modifications. Created a new webform. Set its master page to the MP I just created.

Still, no modifications. No markup. No user controls. No references. Nothing. However when I try to run it, I get:

Content controls have to be top-level controls in a content page or a nested master page that references a master page.
HttpException (0x80004005): Content controls have to be top-level controls in a content page or a nested master page that references a master page.]
   System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection) +8665016
   System.Web.UI.Page.get_Master() +51
   System.Web.UI.Page.ApplyMasterPage() +15
   System.Web.UI.Page.PerformPreInit() +45
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +282

If I do the same exact thing in a standalone project thats outside of this solution, it works fine. Keep in mind that I'm using a web application project vs a website project if that makes any difference.

The webform:

<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Default.aspx.vb" Inherits="WebUI._Default" MasterPageFile="~/Site1.Master" %>

<!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>
</head>
<body>
    <form id="form1" runat="server">
    <div>

    </div>
    </form>
</body>
</html>

The master page:

<%@ Master Language="VB" AutoEventWireup="false" CodeBehind="Site1.master.vb" Inherits="WebUI.Site1" %>

<!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">
    </asp:ContentPlaceHolder>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">

        </asp:ContentPlaceHolder>
    </div>
    </form>
</body>
</html>

Your web form shouldn't have all of that markup (like the <html> tag). Since it has a master page, you just start with the content tag. Your aspx page should look like this:

<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Default.aspx.vb" Inherits="WebUI._Default" MasterPageFile="~/Site1.Master" %>

<asp:content id="Content1" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
   This is the body!
</asp:content>

When you're adding a new aspx page make sure to check "select master page" in the "add new item" dialog.

Here's another way using Visual Studio: If you do New Item in Visual Studio and you select Web Form, it will create a standalone *.aspx web form, which is what you have for your current web form (is this what you did?). You need to select Web Content Form and then select the master page you want attached to it.

Your web form should look like this:

<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Default.aspx.vb" Inherits="WebUI._Default" MasterPageFile="~/Site1.Master" %>
<asp:Content runat="server" ID="head" ContentPlaceHolderId="head">
<!-- stuff you want in &gt;head%lt; -->
</asp:Content>

<asp:Content runat="server" ID="content" ContentPlaceHolderId="ContentPlaceHolder1">
<h1>Your content</h1>
</asp:Content>

Note that there is no <html> tag

When you created the WebForm, did you select the Master page it is attached to in the "Add New Item" dialog itself ? Or did you attach it manually using the MasterPageFile attribute of the @Page directive ? If it was the latter, it might explain the error message you receive.

VS automatically inserts certain markup in each kind of page. If you select the MasterPage at the time of page creation itself, it does not generate any markup except the @Page declaration and the top level Content control.

Master Page Weirdness - "Content controls have to be top-level controls in a content page or a nested master page that references a master page."

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