PowerShell无法使用枚举MultipleInstances

Question

我希望使用Powershell设置＆＃34;如果任务已经运行，则适用以下规则：到＃34;不要启动新实例＆＃34;

我的powershell脚本如下所示：

$Task = Get-ScheduledTask -TaskName "MyJob"
$Task.Settings.MultipleInstances= "StopExisting"
Set-ScheduledTask -User "USER" -Password "PASS" $Task

我收到错误：

Exception setting "MultipleInstances": "Cannot convert value "StopExisting" to type 
"Microsoft.PowerShell.Cmdletization.GeneratedTypes.ScheduledTask.MultipleInstancesEnum". Error: "Unable to match the 
identifier name StopExisting to a valid enumerator name. Specify one of the following enumerator names and try again:
Parallel, Queue, IgnoreNew""

当我将$ Task.Settings.MultipleInstances设置为Parallel，Queue和Ignorenew时，它可以工作。只是＆＃34; StopExisting＆＃34;失败。

来源：https://msdn.microsoft.com/en-us/library/windows/desktop/aa383507(v=vs.85).aspx

我查看了StackOverflow，发现了类似的问题：Powershell New-ScheduledTaskSettingsSet

我将脚本更新为：

$Task = Get-ScheduledTask -TaskName "MyJob"
$StopExisting = New-ScheduledTaskSettingsSet
$StopExisting.CimInstanceProperties['MultipleInstances'].Value = 3
$Task.Settings.MultipleInstances= $StopExisting
Set-ScheduledTask -User "USER" -Password "PASS" $Task

现在我得到了不同的错误：

Exception setting "MultipleInstances": "Cannot convert the "MSFT_TaskSettings3" value of type 
"Microsoft.Management.Infrastructure.CimInstance#Root/Microsoft/Windows/TaskScheduler/MSFT_TaskSettings3" to type 
"Microsoft.PowerShell.Cmdletization.GeneratedTypes.ScheduledTask.MultipleInstancesEnum"."
At C:\temp\PythonService\WatchListPowerShell.ps1:13 char:1
+ $Task.Settings.MultipleInstances= $StopExisting
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], SetValueInvocationException
    + FullyQualifiedErrorId : ScriptSetValueRuntimeException

知道我在这里做错了什么，怎么解决这个问题？

全部谢谢。