رسالة خطأ في ملف config.web

السلام عليكم ورحمة الله وبركاته

عملت مشروع وكان يعمل بشكل سليم ولكن أصبح يظهر رسالة الخطأ

Error	1	Sections must only appear once per config file.  See the help topic <location> for exceptions. (C:\Documents and Settings\root\My Documents\Visual Studio 2005\WebSites\WebSite10\web.config line 28)

مع العلم أن كود مولف الكونفيج هو

<?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>
	<system.web>
		<customErrors mode="Off"/>
	<compilation debug="true"/> 
  </system.web>
	<appSettings/>
	<!--	<connectionStrings/>  -->
	<system.web>
		<!-- 
			Set compilation debug="true" to insert debugging 
			symbols into the compiled page. Because this 
			affects performance, set this value to true only 
			during development.

			Visual Basic options:
			Set strict="true" to disallow all data type conversions 
			where data loss can occur. 
			Set explicit="true" to force declaration of all variables.
		-->

		<compilation debug="true" strict="false" explicit="true" >
			<assemblies>
				<add assembly="Microsoft.VisualBasic.Compatibility, Version=8.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
				<add assembly="System.Windows.Forms, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
			</assemblies>
		</compilation>

		<pages>
			<namespaces>
				<clear/>
				<add namespace="System"/>
				<add namespace="System.Collections"/>
				<add namespace="System.Collections.Specialized"/>
				<add namespace="System.Configuration"/>
				<add namespace="System.Text"/>
				<add namespace="System.Text.RegularExpressions"/>
				<add namespace="System.Web"/>
				<add namespace="System.Web.Caching"/>
				<add namespace="System.Web.SessionState"/>
				<add namespace="System.Web.Security"/>
				<add namespace="System.Web.Profile"/>
				<add namespace="System.Web.UI"/>
				<add namespace="System.Web.UI.WebControls"/>
				<add namespace="System.Web.UI.WebControls.WebParts"/>
				<add namespace="System.Web.UI.HtmlControls"/>
				<!-- <add namespace="system.data.oledb"/>	  -->
			</namespaces>
		</pages>
		<!--
			The <authentication> section enables configuration 
			of the security authentication mode used by 
			ASP.NET to identify an incoming user. 
 		<authentication mode="Windows"/>
	   -->
		<!--
			The <customErrors> section enables configuration 
			of what to do if/when an unhandled error occurs 
			during the execution of a request. Specifically, 
			it enables developers to configure html error pages 
			to be displayed in place of a error stack trace.

		<customErrors mode="RemoteOnly" defaultRedirect="GenericErrorPage.htm">
			<error statusCode="403" redirect="NoAccess.htm" />
			<error statusCode="404" redirect="FileNotFound.htm" />
		</customErrors>
		-->
	</system.web>
	<!--  <appSettings>
	<add key="appStrConnection" value="PWD=pword;UID=webUser;"/>
	</appSettings>  
-->
	<!--<appSettings>
	<add key = "ConnectionString" value = "server = localhost;uid = sa;pwd =;database = DBPerson" />
	</appSettings>
	-->
</configuration>

المشكلة بسطر

<compilation debug="true" strict="false" explicit="true" >