If you want to translate a valid user name to its security identifier (SID), here is a function to do that for you:
function Name2SID($name, $domain=$env:userdomain) { $objUser = New-Object System.Security.Principal.NTAccount($domain, $name) $strSID = $objUser.Translate([System.Security.Principal.SecurityIdentifier]) $strSID.Value }
Try it with your current user name:
Name2SID $env:username