有两种解决方法。
1.请使用32比特的appcmd.exe。范例如下。
设置配置-节：应用程序设置/+"[键=“测试”，值=“测试”]”/commit：webroot /clr：4.0
1.直接在powershell上使用MWA。下面是一个示例。
在此基础上，本文提出了一种新的Web服务器配置方法，该方法包括以下步骤：

经过实验，使用此处提供的答案中的一些信息和脱机对话，我可以得出结论：使用Microsoft WebAdministration PowerShell cmdlet编辑32位根web.config文件 -是不可能的*。
看起来cmdlet被硬编码为只查看64位版本的配置文件。IIS管理器的行为也是如此。我无法解释为什么会出现这种情况。
我还发现使用一些cmdlet编辑64位Clr 2.0网站和应用程序时存在很多问题。Clr参数并不存在于所有cmdlet上，即使在有Clr参数的cmdlet中，它似乎也不总是工作。
因此，我决定放弃WebAdministration cmdlet，直接使用“Microsoft.Web.Administration.dll”程序集和Microsoft.Web.Administration.ServerManager对象。
下面是我编写的一些函数，可能会有帮助：

function Get-MWAConfigObjects
    {
        <#
                .SYNOPSIS
                Returns object to manage IIS configuration in root web.config
                .DESCRIPTION
                The objects returned allow viewing or editing or configuration. Parameters open the appropriate version, either 32 or 64 bit for the appropriate version of the ManagedRunTime. https://msdn.microsoft.com/en-us/library/microsoft.web.administration.servermanager(v=vs.90).aspx
Ensure that you call CommitChanges to save any changes made.
                .EXAMPLE
                $MWA = Get-MWAConfigObjects -ManagedRunTimeVersion v2.0 -Architecture 32               $MWA.Configuration.GetSection('system.web/compilation','MyWebSite/MyApplication').SetAttributeValue('tempDirectory', 'C:\NewPath')
                $MWA.ServerManager.CommitChanges()             
        #>
        [cmdletbinding(positionalbinding = $false)]
        param(
            [Parameter(Mandatory = $True)][string][ValidateSet('v2.0','v4.0')] $ManagedRunTimeVersion,
            [Parameter(Mandatory = $True)][string][ValidateSet(32,64)] $Architecture
        )

        $assemblyPath = $(Join-Path -Path $([System.Environment]::GetFolderPath('System')) -ChildPath $(Join-Path -Path 'inetsrv' -ChildPath 'Microsoft.Web.Administration.dll'))
        If (Test-Path -Path $assemblyPath -PathType Leaf)
        {
            $null = [System.Reflection.Assembly]::LoadFrom($assemblyPath)
            $iis = New-Object -TypeName Microsoft.Web.Administration.ServerManager
            $wcm = New-Object -TypeName Microsoft.Web.Administration.WebConfigurationMap -ArgumentList $(Get-ConfigFilePath -Type machine -ManagedRunTimeVersion $ManagedRunTimeVersion -Architecture $Architecture), $(Get-ConfigFilePath -Type web -ManagedRunTimeVersion $ManagedRunTimeVersion -Architecture $Architecture)
            $configuration = $iis.GetWebConfiguration($wcm, $null)

            $object = New-Object -TypeName PSObject
            $object | Add-Member -MemberType NoteProperty -Name ServerManager -Value $iis
            $object | Add-Member -MemberType NoteProperty -Name Configuration -Value $configuration
            Write-Output -InputObject  $object
        }
        else
        {
            Throw "Cannot validate existence of required assembly 'Microsoft.Web.Administration.dll' at ""$assemblyPath"""
        }
    }

    function Get-ConfigFilePath
    {
        [CmdletBinding(PositionalBinding = $false)]
        param
        (
            [Parameter(Mandatory = $True)][string][ValidateSet('web','machine')] $Type, 
            [Parameter(Mandatory = $True)][string][ValidateSet('v2.0','v4.0')] $ManagedRunTimeVersion, 
            [Parameter(Mandatory = $True)][string][ValidateSet(32,64)] $Architecture
        )

        $ErrorActionPreference = 'stop'

        switch ($ManagedRunTimeVersion)
        {
            'v2.0'
            {
                switch ($Architecture)
                {
                    32
                    {
                        $path = $(Join-Path -Path $([System.Environment]::GetFolderPath('Windows')) -ChildPath "Microsoft.NET\Framework\v2.0.50727\CONFIG\$Type.config")
                        break
                    }
                    64
                    {
                        $path = $(Join-Path -Path $([System.Environment]::GetFolderPath('Windows')) -ChildPath  "Microsoft.NET\Framework64\v2.0.50727\CONFIG\$Type.config")
                        break
                    }
                }

                break;
            }
            'v4.0'
            {
                switch ($Architecture)
                {
                    32
                    {
                        $path = $(Join-Path -Path $([System.Environment]::GetFolderPath('Windows')) -ChildPath "Microsoft.NET\Framework\v4.0.30319\CONFIG\$Type.config")
                        break
                    }
                    64
                    {
                        $path = $(Join-Path -Path $([System.Environment]::GetFolderPath('Windows')) -ChildPath  "Microsoft.NET\Framework64\v4.0.30319\CONFIG\$Type.config")
                        break
                    }
                }

                break;
            }
        }

        If (Test-Path -Path $path -PathType Leaf)
        {
            Write-Output -InputObject $path
        }
        else
        {
            Throw "Cannot validate configuration file at path ""$path"""
        }
    }