added namespace in web.config but still prompt error

Hi, I am using .NET 2.0 and created a simple default.aspx ... I added the namespace in web.config but when i try to run the website, it gives me this error :
Web.config
------------------------------
<?xml version="1.0"?>
<!--
    Note: As an alternative to hand editing this file you can use the
    web admin tool to configure settings for your application. Use
    the Website->Asp.Net Configuration option in Visual Studio.
    A full list of settings and comments can be found in
    machine.config.comments usually located in
    \Windows\Microsoft.Net\Framework\v2.x\Config
-->
<configuration>
    <appSettings/>
    <connectionStrings>
        <add name="ConnectionString" connectionString="Data ...