Configuration Error 'membership' already defined.问题出在哪里

最近牛头一直出现这样一个错误：
 

Server Error in '/' Application.

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Configuration Error

Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: Section or group name 'membership' is already defined. Updates to this may only occur at the configuration level where it is defined.

Source Error:

Line 7:  		
Line 8:  		<sectionGroup name="system.web">
Line 9:  			<section name="membership" type="Microsoft.ScalableHosting.Configuration.MembershipConfigHandler, MemberRole, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b7c773fb104e7562" />
Line 10: 			<section name="roleManager" type="Microsoft.ScalableHosting.Configuration.RolesConfigHandler, MemberRole, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b7c773fb104e7562" />
Line 11: 			<section name="profile" type="Microsoft.ScalableHosting.Configuration.ProfileConfigHandler, MemberRole, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b7c773fb104e7562" />

Source File: k:\mainhostweb\na57\web\web.config    Line: 9

Show Additional Configuration Errors:

Section or group name 'roleManager' is already defined. Updates to this may only occur at the configuration level where it is defined. (k:\mainhostweb\na57\web\web.config line 10)

Section or group name 'profile' is already defined. Updates to this may only occur at the configuration level where it is defined. (k:\mainhostweb\na57\web\web.config line 11)

Section or group name 'anonymousIdentification' is already defined. Updates to this may only occur at the configuration level where it is defined. (k:\mainhostweb\na57\web\web.config line 12)

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Version Information: Microsoft .NET Framework Version:2.0.50727.42; ASP.NET Version:2.0.50727.42

这个错误让我迷惑了很久，配置文件以前一直好好的啊，怎么突然就出问题了呢？经过多方考察，我才发现，原来是.NET Framework的版本升为2.0了。按照http://communityserver.org/forums/476116/ShowPost.aspx 上介绍的方法，把版本换回1.1就可以解决这个问题。