robocopy无法找到指定的路径

Question

#Variables
$logfile = "\\hermamora\Public\Plex Backup\Logs\Plex_Backup_Log_$(get-date -format "yyyyMMdd").txt"

function log($string, $color)
{
   if ($Color -eq $null) {$color = "white"}
   Write-Host $string -ForegroundColor $color
   $string | Out-File -Filepath $logfile -Append
}

function Main {
    robocopy Q:\ L:\ /v /mir /z /r:1 /w:5 
}
$main = Main

#Arguments for Email
$From = "FROMADDRESS"
$To = "TOADDRESS"
#$Attachment = $logfile
$Subject = "Plex Backup Success"
$Body = "Here is the log of the Plex DB Backup, It was able to complete successfully"
$SMTPServer = "smtp.gmail.com"
$SMTPPort = "587"
$login = "USERNAME"
$password = "PASSWORD" | ConvertTo-SecureString -AsPlainText -Force
$credentials = New-Object System.Management.Automation.Pscredential -Argumentlist $login,$password

#Main Script

#Sets up Drives for Easy copy
subst L: "\\hermamora\Public\Plex Backup\Backup" 
subst Q: "C:\Users\ztownes\AppData\Local\Plex Media Server"

#Stops Plex and Copies DB
taskkill /IM "Plex Media Server.exe" 
Start-Sleep -Seconds 15
log $main
Start-Sleep -Seconds 15
Start-process "C:\Program Files (x86)\Plex\Plex Media Server\Plex Media Server.exe" 

#Removes Drives for unclutering
subst /d L:
subst /d Q:
Start-Sleep -Seconds 5

#Sends Email
Send-MailMessage -From $From -To $To -Cc $Cc -Subject $Subject -Body $Body -SmtpServer $SMTPServer -Port $SMTPPort -UseSsl -Credential $credentials -Attachments $logfile

Start-Sleep -Seconds 5

每当我尝试运行此代码时，都无法找到驱动器L：和Q：for robocopy。我能够在Windows资源管理器中看到驱动器。我有一个几乎完全相同的PowerShell脚本运行它没有问题。出于明显的安全原因，我已从电子邮件参数中删除了电子邮件地址和密码。