在web.config中加密成员身份元素时出现问题

我正在尝试加密.NET应用程序的web.config中的“system.web.membership”元素,以保护Active Directory的用户名和密码。我正在使用aspnet_regiis命令进行加密,并尝试了几个不同的字符串来获取“pe”选项的值,但没有成功。我已经成功地加密了web.config上的“connectStrings”元素。

CMD

C:\Windows\Microsoft.NET\Framework\v2.0.50727>aspnet_regiis -pe "connectionStrings" -site MySite -app /MyApp
Encrypting configuration section...
Succeeded!

C:\Windows\Microsoft.NET\Framework\v2.0.50727>aspnet_regiis -pe "membership" -site MySite -app /MyApp
Encrypting configuration section...
The configuration section 'membership' was not found.
Failed!

C:\Windows\Microsoft.NET\Framework\v2.0.50727>aspnet_regiis -pe "system.web.membership" -site MySite -app /MyApp
Encrypting configuration section...
The configuration section 'system.web.membership' was not found.
Failed!

Web.CONFIG

<configuration>
    ...
    <system.web>
        ...
        <authentication mode="Forms">
            <forms name=".ADAuthCookie" 
                   timeout="30"/>
        </authentication>
        <authorization>
            <deny users="?"/>
            <allow users="*"/>
        </authorization>
        <membership defaultProvider="MyADMembershipProvider">
            <providers>
                <add name="MyADMembershipProvider"
                     type="System.Web.Security.ActiveDirectoryMembershipProvider, System.Web, Version=2.0.0.0,Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" 
                     connectionStringName="ADConnectionString" 
                     connectionUsername="MyUserName" 
                     connectionPassword="MyPassowrd"/>
            </providers>
        </membership>
        ...
    </system.web>
    ...
</configuration>

那给了什么?我错过了什么?