unale to open the design page in asp.net

<%@ Master Language="C#" EnableViewState="true" MasterPageFile="~/cERP.master" AutoEventWireup="true"
Inherits="WebForms_Templates_BasicTemplate" CodeBehind="BasicTemplate.master.cs" %>

<asp:Content ID="Content1" runat="server" ContentPlaceHolderID="Menu">
<div id="divBasicTemplate">
<asp:ContentPlaceHolder ID="MainBasicContent" runat="server">
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
<contenttemplate>
<telerik:RadTabStrip ID="radTabStripBasic" runat="server" MultiPageID="RadMultiPageBasic"
SelectedIndex="0" önTabClick="RadTabStrip1_TabClick">
<tabs>
<telerik:radtab text="<u>A</u>ccount Details" selectedindex="0" accesskey="A" selected="True"
="" value="radTabMainAccountDetails">

<telerik:radtab text="<u>A</u>ddress Details" accesskey="A" value="radTabAddressDetails">

<telerik:radtab text="<u>C</u>ontact Details" accesskey="C" value="radTabContactDetails">

<telerik:radtab text="<u>S</u>upplier Details" accesskey="S" value="radTabSupplierDetails">

<telerik:radtab text="S<u>u</u>pplier Items" accesskey="S" value="radTabSupplierItems">

<telerik:radtab text="<u>T</u>ax Details" accesskey="T" value="radTabTaxDetails">

<telerik:radtab text="<u>B</u>ank Details" accesskey="B" value="radTabBankDetails">

<telerik:radtab text="<u>L</u>ist" visible="false" accesskey="L" value="radTabList">



<table width="100%">
<tr style="background-color: #C0C0C0">
<td width="92%" align="center" valign="middle">
<asp:Label ID="lblFormName" runat="server" Font-Bold="True" Font-Names="Times New Roman"
Font-Size="Large">
</td>
<td width="8%" valign="middle" align="center">
Show List
</td>
</tr>
</table>
<asp:Label ID="lblError" runat="server" Style="text-align: left" Text="Error Message"
Width="100%">
<telerik:RadMultiPage ID="RadMultiPageBasic" runat="server" SelectedIndex="0" ScrollBars="Auto"
class="RadMultiPage">
<telerik:RadPageView ID="radPageViewAccountDetails" runat="server">
<table id="MainTable" style="width: 100%;">
<tr>
<td style="width: 117px;">
<asp:Label ID="lblSerialNo" runat="server" Font-Bold="False" TabIndex="1" Text="Serial No:"
AccessKey="S" BackColor="#C0C0C0">
</td>
<td style="width: 159px">
<telerik:RadTextBox ID="SerialNo" runat="server" LabelCssClass="" Width="180px">

Design Part is showing lot of "Error Creating Control" labels in red colour.

hi..............
what about my querry!!!!!!!!!!!