Invoke-Command: Null-value and positional parameter errors - powershell

Question

I wanted to start a new thread for this, since I am using a different method in my code now. I have written a script that pings hundreds of devices and logs their online or offline status. It was taking an extremely long time to run, so I am now looking into using Invoke-Command to run the commands remotely on servers for each site (instead of all from the same server). I am receiving the following errors: "A positional parameter cannot be found that accepts argument 'Of'", "You cannot call a method on a null-valued expression", and this is happening for each server as it is iterating through them. Any ideas as to why this is happening? Thank you very much, here is my current code:
<#
.NOTES
===========================================================================
Created on: 11/17/2016 8:06 AM
Created by:
Organization:
Filename: Get-MPOSOfflinePrinters.ps1
===========================================================================
.DESCRIPTION
#>
#Define log file variables and remove any existing logs
$logfile = "D:\Logs\MPOSPrinterPingLog.txt"
$offlineprinters = "D:\Reports\MPOS\MPOSOfflinePrinters.txt"
If (Test-Path $logfile) {Remove-Item $logfile}
If (Test-Path $offlineprinters) {Remove-Item $offlineprinters}
Add-Content $logfile "Gathering server list"
#Compiling list of all MPOS Print Servers
$serverList = (Get-ADComputer -Filter "Name -like 'Q0*P30' -or Name -like 'Q0*P32'" -SearchBase "OU=Print,OU=Prod,OU=POS,DC=COMPANY,DC=NET").name | Sort-Object | Out-File C:\Temp\MPOS\MPOSPrintServers.txt
$serverListPath = "C:\Temp\MPOS\MPOSPrintServers.txt"
Add-Content $logfile "Compiling text file"
#Retrieve a list of MPOS Print servers from text file and set to variable $serverNames
$serverNames = Get-Content -Path $serverListPath
Invoke-Command -ComputerName $serverNames -ScriptBlock {
#Define log file variables and remove any existing logs
$logfile = "C:\Temp\MPOSPrinterPingLog.txt"
$offlineprinters = "C:\Temp\MPOSOfflinePrinters.txt"
$masteroffline = "\\a0345p689\d$\Reports\MPOS\MPOSOfflinePrinters.txt"
If (Test-Path $logfile) {Remove-Item $logfile}
If (Test-Path $offlineprinters) {Remove-Item $offlineprinters}
#process xml file to parse IP addresses for ping
$timestamp2 = (Get-Date -Format g)
Add-Content $logfile "$timestamp2 - Processing xml file from $serverName to parse data to csv"
$xml = [xml](Get-Content C:\ProgramData\Microsoft\Point Of Service\Configuration\Configuration.xml)
$PrinterNames = $xml.selectNodes('//PointOfServiceConfig/ServiceObject/Device') | foreach {New-Object -TypeName psobject -Property #{LogicalName=$_.LogicalName.Name}}
$PrinterIPs = $xml.selectNodes('//PointOfServiceConfig/ServiceObject/Device') | foreach {New-Object -TypeName psobject -Property #{HardwarePath=$_.HardwarePath}}
foreach ($PrinterIP in $PrinterIPs) {
$pingableIP = $PrinterIP.HardwarePath
If (Test-Connection $pingableIP -Quiet -Count 1) {
$timestamp3 = (Get-Date -Format g)
Add-Content $logfile "$timestamp3 - $serverName, $pingableIP is online and pingable"
}
Else {
$timestamp3 = (Get-Date -Format g)
Add-Content $offlineprinters "$timestamp3 - $serverName, $pingableIP is offline!"
}
Get-Content $offlineprinters | Out-File -FilePath $masteroffline -Append -NoClobber
} #foreach ($PrinterIP in $PrinterIPs) {
} #Invoke-Command -ComputerName $serverNames -ScriptBlock {