Getting Access Denied, PSSessionStateBroken error

Hello, running the following script and receiving this error when trying to get information from remote servers. I can run the script myself and don't receive any errors, its only PRTG that is returning the error so I believe that it has something to do with the way PRTG is running the script. I have the correct credentials put in for the sensor, but other than that i'm not sure what could be the issue.

$hostname = "yourhostname"

Invoke-Command -ComputerName $hostname{
$today=(Get-Date)
$dateshift=(Get-Date).AddHours(-12)
$EventError=Get-WinEvent -LogName Microsoft-Windows-Backup| Where-Object {$_.TimeCreated -gt $dateshift} | Where-Object {$_.LevelDisplayName -eq "Error"}
$EventWarning=Get-WinEvent -LogName Microsoft-Windows-Backup| Where-Object {$_.TimeCreated -gt $dateshift} | Where-Object {$_.LevelDisplayName -eq "Warning"}
$EventOK=Get-WinEvent -LogName Microsoft-Windows-Backup| Where-Object {$_.TimeCreated -gt $dateshift} | Where-Object {$_.LevelDisplayName -eq "Information"}

$backupsets=Get-WBBackupSet
$lastbackup=(Get-Date)-($backupsets.BackupTime |Measure-Object -Maximum |Select-Object -ExpandProperty Maximum)
$lastbkround=[math]::Floor($lastbackup.TotalHours)

$x = [string] $($EventError.Count)+":OK"
Write-Host $x



Exit 0
} 

exe powershell prtg-custom-sensor script windows-backup