在PS脚本中接收奇怪的错误消息

Question

我有一个PowerShell脚本，可以抓取远程计算机上当前登录的用户并获取其本地配置文件C：\ users \ USERNAME \ documents，pictures，music等的总大小。我已确认远程计算机在线并且用户已登录。当脚本正在运行时，从它获取文件夹大小的意义上来说，它会返回以下消息：

Get-WmiObject : Invalid parameter
At C:\Users\administrator\Desktop\get_folder_size.ps1:4 char:9
+ $user = Get-WmiObject Win32_ComputerSystem -ComputerName $system | Se ...
+         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [Get-WmiObject], ManagementException
    + FullyQualifiedErrorId : GetWMIManagementException,Microsoft.PowerShell.Commands.GetWmiObjectCommand

You cannot call a method on a null-valued expression.
At C:\Users\administrator\Desktop\get_folder_size.ps1:5 char:1
+ $pos = $user.IndexOf("\")
+ ~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

You cannot call a method on a null-valued expression.
At C:\Users\administrator\Desktop\get_folder_size.ps1:6 char:1
+ $user = $user.Substring($pos+1)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

我很困惑，因为如果我正确阅读邮件，它应该无法获取用户名，因此无法获得正确的文件夹和大小。

以下是我正在运行的代码

foreach ($system in Get-Content "C:\net_view.txt")
{
    $colItems = 0
    $user = Get-WmiObject Win32_ComputerSystem -ComputerName $system |
            Select-Object -ExpandProperty UserName
    $pos  = $user.IndexOf("\")
    $user = $user.Substring($pos+1)

    $path = $system +"\c$\users\" + $user

    $colItems = (Get-ChildItem $path -Recurse -ErrorAction SilentlyContinue |
                Measure-Object -property length -sum)
    "{0:N2}" -f ($colItems.sum / 1MB) + " MB"

    Add-Content C:\users\administrator\desktop\profile_size.txt ($colItems.sum / 1MB)
    Add-Content C:\users\administrator\desktop\profile_size.txt $system
}