只允许在包含内容控件错误的内容页面中直接使用内容控件

Question

我一直在制作带有母版页的网页表单，我遇到了错误：只允许内容控件直接放在包含内容控件的内容页面中。现在我已经调查了不同的论坛，我无法找到解决方案。这从来没有出现在我面前，而且很奇怪，因为我每次做的都是一样的 这是代码：

<%@ Page Title="" Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Register.aspx.cs" Inherits="Register" %>

<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
     <script>
        function CheckAll()
{
  var flag = true;
  var length = document.getElementById('user').value.length;
  var value = document.getElementById('user').value;
  for (var i = 0; i < length; i++) {
    if (!((value.charAt(i) >= '0' && value.charAt(i) <= '9') || (value.charAt(i) >= 'a' && value.charAt(i) <= 'z') || (value.charAt(i) >= 'A' && value.charAt(i) <= 'Z'))) {
      alert("username must be made of characters and numbers only");
      return false;
    }
  }
  var lengthPass = document.getElementById('password').value.length;
  var valuePass = document.getElementById('password').value;
  for (var i = 0; i < lengthPass; i++) {
    if (!((valuePass.charAt(i) >= '0' && valuePass.charAt(i) <= '9') || (valuePass.charAt(i) >= 'a' && valuePass.charAt(i) <= 'z') || (valuePass.charAt(i) >= 'A' && valuePass.charAt(i) <= 'Z'))) {
      alert("Password must be made of characters and numbers only");
      return false;
    }

  }
        if (!(length >= 6 || length <= 20))
        {
    alert("Username Must be 6-20 Characters long");
    return false;
  }
        if (!(lengthPass >= 6 || lengthPass <= 20))
        {
            alert("Password must be 6-20 characters long")
            return false;
        }


        var x = document.forms["form"]["mail"].value;
        var atpos = x.indexOf("@");
        var dotpos = x.lastIndexOf(".");
        if (atpos < 1 || dotpos < atpos + 2 || dotpos + 2 >= x.length) {
            alert("Not a valid e-mail address");
            return false;
        }
            var valuePhone = document.getElementById('phone').value;
            var lengthPhone = document.getElementById('phone').value.length;
            for (var i = 0; i < length; i++)
            {
                if (!((valuePhone.charAt(i) >= '0' || valuePhone.charAt(i) <= '9')))
                {
                    alert("phone number must be made of numbers only");
                    return false;
                }
            }
            if (lengthPhone != 10)
            {
                alert("phone number must be 10 numbers long");
            }



  return true;
}




    </script>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <form id="form" runat="server">
        Name+Last Name: <input type="text" name="names" id="name" />
        <br />
        <br /> Username: <input type="text" name="username" id="user" />
        <br />
        <p style="font-size:70%">must contain 6-20 character</p>
        <br /> Password: <input type="text" name="password" id="password" />
        <br />
        <p style="font-size:70%">must contain 6-20</p>
        <br /> E-mail: <input type="text" name="mail" id="mail" />
        <br /> Phone Number: <input type="text" name="phone" id="phone" />
        <br /> Enter Your Birth Date:
        <br /> 
        <input type="date" name="date" id="date"/>
        <br />
        <br /> Enter Your Favourite Esports Game:
        <select name="choose" id="choose">
            <option>League Of Legends</option>
            <option>Dota</option>
            <option>StarCraft</option>
            <option>Street Fighter</option>
            <option>Smite</option>
            <option>Mortal Kombat</option>
            <option>Heroes Of The Storm</option>
            <option>Super Smash Bros</option>
            <option>Call of Duty</option>
            <option>Counter Strike: Global Offensive</option>
            <option>I Dont Watch Esports</option>
        </select>

        <table border="1">
            <tr>
                <th>
                    <a href="HomePage.html" style="color:red">To Get Back To The Home Page</a>
                </th>
            </tr>
        </table>
        <br />
        <br />
        <input type="checkbox" name="agree" id="agree" value="check validity" onclick="AgreeCheck()" />
        <input type="submit" name="sub" id="sub" value="submit" disabled />
    </form>
    <script>
           function AgreeCheck() {
               document.getElementById("agree").checked = CheckAll();
               document.getElementById("sub").disabled = !CheckAll();
           }
    </script>
</asp:Content>