Parallel processing using Scriptblock not working from windows task scheduler

Hi,

I am using scriptblock to run parallel commands. My code is working correctly when I am running directly from PowerGUI IDE, but when I schedule it inwindows task scheduler or Visualcron, it's only processing first 4 commands and then stopping. Why this happening? Is there any conflict with Scriptblock with windows task scheduler? Is there anything that is destroying the Scriptblock after running the first instance of 4 threads? How can I fix this problem? I need to implement my code in production as soon as possible, but no way I am able to make it working from task scheduler. Any help?

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## Run commands in parallel
$MaxThreads = 4
$SleepTimer = 1000

## Array contains 20 commands
$Commands = @()

## Parallel run block
## ===================================================
ForEach ($Command in $Commands)
{
   While (@(Get-Job -state running).count -ge $MaxThreads)
   {      
   Start-Sleep -Milliseconds $SleepTimer
   }

   Start-Job -scriptblock {
   $objProcess = New-Object System.Diagnostics.Process
   $objProcess.StartInfo = New-Object System.Diagnostics.ProcessStartInfo
   $objProcess.StartInfo.FileName = "C:\Program Files (x86)\SPSS\perfcalc.exe"
   $objProcess.StartInfo.Arguments = $args[0]
   $objProcess.StartInfo.UseShellExecute = $shell
   $objProcess.StartInfo.WindowStyle = 1
   $objProcess.StartInfo.RedirectStandardOutput = $true
   $null = $objProcess.Start()
   $objProcess.WaitForExit()
   $exitcode = $objProcess.ExitCode
   $objProcess.Dispose()

   if ($exitcode -ne 0)
   {
   throw "Error{0}" -f ([string] $exitcode)
   }
   } -ArgumentList $Command -Name $Command | Out-Null

}

While (@(Get-Job -State Running).count -gt 0)
{
    Start-Sleep -Milliseconds $SleepTimer
}

$Results = ""
foreach ($Job in Get-Job)
{
    if ($Job.State -eq 'Failed') 
{
$Results += $Job.Name + ($Job.ChildJobs[0].JobStateInfo.Reason.Message)
}
else
{
        Write-Host (Receive-Job $Job)
}
}

ForEach($Job in Get-Job)
{
    Remove-job -Force $Job
}