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

<%@ Page Title="" Language="C#" MasterPageFile="~/Master/MasterPage.master" AutoEventWireup="true" CodeFile="ExcelToSqlDB.aspx.cs" Inherits="DMS_ExcelToSqlDB" %>
<%@ Register TagPrefix="rad" Namespace="Telerik.WebControls" Assembly="RadCalendar.NET2" %>
<%@ Register Src="../CommonControls/MsgBox.ascx" TagName="MsgBox" TagPrefix="uc1" %>
<asp:Content ID="Content1" ContentPlaceHolderID="PlaceHolderMain" Runat="Server">
<p>
        <uc1:MsgBox ID="Msgbox1"  runat="server" />
    </p>
    <p>
        <table cellpadding="3" cellspacing="1" style="width: 75%" align="center">
            <tr>
                <td align="center" bgcolor="Black" style="width: 363px">
                     </td>
                <td align="center" bgcolor="Black">
                     </td>
            </tr>
            <tr>
                <td style="width: 363px" align="right">
                    Browse:</td>
                <td>
                    <asp:FileUpload ID="fupExcel" runat="server" />
 
                    <asp:Button ID="btnGetExcel" runat="server" Text="Get Excel Sheet" />
                </td>
            </tr>
            <tr>
                <td style="width: 363px" align="right">
                    <asp:Label ID="lblsheet" runat="server" Text="Sheet Name : "></asp:Label>
                <td>
                    <asp:DropDownList ID="ddlSheet" runat="server" AutoPostBack="True" 
                        Visible="False">
                    </asp:DropDownList>
                </td>
            </tr>
            <tr>
                <td style="width: 363px">
                     </td>
                <td>
                    <asp:Button ID="btnFetch" runat="server" Text="Fetch" Visible="False" />
         
                    <asp:Button ID="btnUpload" runat="server" Text="Upload" Visible="False" />
                </td>
            </tr>
        </table>
        <br />
    </p>
    <table style="width: 100%">
        <tr>
            <td>
        <asp:GridView ID="grvMaterial" runat="server" AllowPaging="True"
        OnRowDataBound="grvMaterial_RowDataBound" HorizontalAlign="Center"
                     EmptyDataText="No/Invalid Records Found Pls. Check" 
            BackColor="White" GridLines="Vertical" BorderColor="#999999" BorderStyle="Solid" 
                    BorderWidth="1px" CellPadding="3" ForeColor="Black" PageSize="8">
            <AlternatingRowStyle BackColor="#CCCCCC" />
            <Columns>
                     <asp:TemplateField HeaderText="Serial number">
                    <ItemTemplate>
                        <asp:Label ID="lblSerial" runat="server"></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>
                     </Columns>
            <FooterStyle BackColor="#CCCCCC" />
            <HeaderStyle BackColor="Black" Font-Bold="True" ForeColor="White" />
            <PagerStyle BackColor="#999999" ForeColor="Black" HorizontalAlign="Center" />
            <SelectedRowStyle BackColor="#000099" Font-Bold="True" ForeColor="White" />
            
          
        </asp:GridView>
            </td>
        </tr>
    </table>
    <p>
    </p>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="PlaceHolderPageTitle" Runat="Server">
</asp:Content>