I am running the following code as part of a scheduled task; the
objective of the code is to determine whether or not someone is logged
on to the workstation in an interactive session, and if so, if that
person is the same one as the one running the task.

ManagementScope ms = new ManagementScope(ManagementPath.DefaultPath);
System.Management.ManagementObject o;
SelectQuery q = new SelectQuery("Win32_LoggedOnUser"); // only
interactive logons
ManagementObjectSearcher query = new ManagementObjectSearcher(ms, q);

ManagementObjectCollection queryCollection = query.Get();
LinkedList<UserInfo> users = new LinkedList<UserInfo>();

foreach (ManagementObject loggedOnUser in queryCollection)
{
 //  Dependent is a Win32_LoginSession object
 ManagementObject session = new
ManagementObject(loggedOnUser["Dependent"].ToString());
 if ((session["LogonType"].ToString()) == "2")  {  // is
interactive?
   //  Antecedent is a Win32_Account object
   Console.WriteLine("About to access the antecedent");
   ManagementObject account = new

ManagementObject(loggedOnUser["Antecedent"].ToString());

   String loginID = session["LogonID"].ToString();

   String SID = account["SID"].ToString();

When this code is run by the logged on user within Visual Studio, it
works fine.  But, when it's run as a scheduled task, running as
Administrator while another user is logged in, an NotFound exception
is thrown when trying to access the "SID" property of the account
object; actually, attempts to access any properties of this object
fail.  Accesses to the properties of the session object are
successful.

Does anyone know why this would be the case?

Thanks in advance,
Ryan