Argument Passed into ScriptBlock Doesn't Work on Last Iteration - powershell

Question

I'm using the following script to run through all of the servers in a specified Active Directory OU and log out the specified user. This runs perfectly well for the first 35 servers but always errors out on the very last server it iterates through. The error is:
Program 'quser.exe' failed to run: Object reference not set to an instance of an object. At line:6 char:24
+ $result = (quser $userAccount)
+ ~~~~~~~~~~~~~~~~~~.
At \\path\to\script.ps1:79 char:5
+ invoke-command -ComputerName $server -ScriptBlock $scriptBlock -A ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : OperationStopped: (Program 'quser....~~~~~~~~~~~~~~.:String) [], RuntimeException
+ FullyQualifiedErrorId : Program 'quser.exe' failed to run: Object reference not set to an instance of an object.At line:6 char:24
+ $result = (quser $userAccount)
+ ~~~~~~~~~~~~~~~~~~.
My reading of the error is that it thinks $userAccount has no value. Is that correct and, if so, can anyone point at what I'm missing? Thank you in advance!
Write-Host " "
Write-Host "This script will log out all active sessions for the specified user. Proceed with caution." -ForegroundColor Black -BackgroundColor Yellow
Write-Host " "
$servers = [System.Collections.ArrayList]::new()
foreach ($server in (Get-ADComputer -SearchBase "OU=FictionalDepartment,DC=Company,DC=net" -Filter "OperatingSystem -like 'Windows Server*'" -Properties Name | select -ExpandProperty name))
{
$servers.add($server) | Out-Null
}
$servers.Sort()
$userAccount = Read-Host "Enter account to log out"
Write-Host " "
foreach ($server in $servers)
{
$scriptBlock = {
param($userAccount)
$ErrorActionPreference = 'Stop'
try
{
$result = (quser $userAccount)
$session = ((quser $userAccount)[1] -split "\s+")[2]
logoff $session
Write-Host " The user was logged into session #$session. They have been LOGGED OFF." -ForegroundColor Yellow
}
catch
{
if ($_.Exception.Message -match 'No user exists')
{
Write-Host " User is not logged in." -ForegroundColor Green
}
else
{
throw $_.Exception.Message
}
}
}
Write-Host "$server"
Invoke-Command -ComputerName $server -ScriptBlock $scriptBlock -ArgumentList $userAccount
$session = $null
}

Answer 1

Based on feedback, I modified the script so that it no longer uses Invoke-Command, but parses the active sessions by running quser <user> /SERVER:<server> as follows:
Write-Host "Will log specified user out of all servers..." -ForegroundColor Black -BackgroundColor Yellow
Write-Host " "
$servers = [System.Collections.ArrayList]::new()
foreach ($server in (Get-ADComputer -SearchBase "OU=Fictional,DC=Company,DC=net" -Filter "OperatingSystem -like 'Windows Server*'" -Properties Name | select -ExpandProperty name))
{
$servers.add($server) | Out-Null
}
$servers.Sort()
$userAccount = Read-Host "Enter account to scan for"
Write-Host ""
foreach ($server in $servers)
{
Write-Host "$server"
$ErrorActionPreference = 'Stop'
try
{
$session = ((quser $userAccount /SERVER:$server)[1] -split "\s+")[3]
logoff /SERVER:$server $session
Write-Host " The user was logged into session #$session. They have been LOGGED OFF." -ForegroundColor Yellow
}
catch
{
if ($_.Exception.Message -match 'No user exists')
{
Write-Host " User is not logged in." -ForegroundColor Green
}
}
}