title: Run many users login at same time, always passed half and fail half in the controller
body: <p>I setup a scenario in loadrunner controller to setup one group with 10 users login at same time, setup parameters with username as 10 usernames, setup parameters run the "next row" with "Unique".</p>
  
  <ol>
  <li>if start 10 Vusers simultaneously till run completion. I got 5 users passes, 5 users failed.</li>
  <li>if start 8 Vusers simultaneously till run completion. I got 4 users passes, 4 users failed.</li>
  <li>if start 6 Vusers simultaneously till run completion. I got 3 users passes, 3 users failed.</li>
  </ol>
  
  <p>Anyone know why that happens? My testcase just needs to run 10 users login at same time.</p>