When you attempt to log in to vCenter Server using the vSphere Web Client, the login fails with a duplicate session error.


When you attempt to log in using the vSphere Web Client, you see an error message similar to the following:

4/19/2012 15:48:45.416 [ERROR] ErrorNotificationManager: faultCode:Server.Processing.DuplicateSessionDetected faultString:'Detected duplicate HTTP-based FlexSessions, generally due to the remote host disabling session cookies. Session cookies must be enabled to manage the client connection correctly.' faultDetail:'null'


This error occurs if the vSphere Web Client service was restarted or upgraded while you had the vSphere Web Client UI open in a Web browser.


  1. Close the Web browser completely.
  2. Relaunch the Web browser.
  3. Go to the vSphere Web Client URL and log in.