Powershell scripting1 - powershell

Question

I am running this Script to get the directory listing
It was working few days ago but I keep having this error
New-PSSession : Cannot validate argument on parameter 'ComputerName'. The argument is null or empty.
Provide an argument that is not null or empty, and then try the command again.
At C:\DEV\Powershell3\directory-listing.ps1:11 char:38
+ $session=New-PSSession -ComputerName $servers
+ ~~~~~~~~
+ CategoryInfo : InvalidData: (:) [New-PSSession], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.PowerShell.Commands.NewPSSessionCommand
Invoke-Command : Cannot validate argument on parameter 'Session'. The argument is null or empty.
Provide an argument that is not null or empty, and then try the command again.
At C:\DEV\Powershell3\directory-listing.ps1:31 char:25
+ Invoke-Command -Session $session -ScriptBlock $scb
+ ~~~~~~~~
+ CategoryInfo : InvalidData: (:) [Invoke-Command], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.PowerShell.Commands.InvokeCommandCommand
$servers=get-content C:\temp\servers.txt
$session=New-PSSession -ComputerName $servers
$scb = {
Write-host "working on $env:COMPUTERNAME" -ForegroundColor Red
$volumes=Get-WmiObject win32_volume -Filter "drivetype=3"
foreach($volume in $volumes) {
$driveletter=$volume.driveletter
if($driveLetter -ne $null) {
$drivename=$volume.name
(Get-ChildItem -path $drivename -Directory) |Select-Object Name,FullName
}
}
}
Invoke-Command -Session $session -ScriptBlock $scb