I am trying to start a process as the LocalSystem account using this code

    ProcessStartInfo _startInfo = new ProcessStartInfo(commandName);
_startInfo.UseShellExecute = false;
_startInfo.UserName = @"NT AUTHORITY\SYSTEM";
_startInfo.CreateNoWindow = true;
_startInfo.Arguments = argument;
_startInfo.RedirectStandardOutput = true;

using (Process _p = Process.Start(_startInfo)) {
  _retVal = _p.StandardOutput.ReadToEnd();
  _p.WaitForExit();
}

But I am getting always the same error message saying "Logon failure: unknown user name or bad password". The user calling the function is a local admin and should be able to start a process with local system privilege. I also tried different combination but no luck.

I would appreciate any help. Thanks