Unable to Logoff XenApp 6.5 ICA session

While growing our XenApp 6.5 environment I noticed certain users were not be able to log off and would receive the message “Waiting for System Event Notification Service”.  Immediately when this occurred, other users would start seeing similar issues from the same XenApp server.


  • Windows 2008 R2
  • XenApp 6.5
  • UPM 4.1
  • vSphere 4.0 <-  What the heck? I know, I know :P
  • Office Communicator 2007 R2


The screen remains unresponsive with the “Waiting for System Event Notification Service” pop-up. On the server user has a Communicator (OCS) running and one of the instances is pegging an entire core resulting in users unable to log off sessions.

This will occur when multiple users try to log off a terminal server at the same time while signed in to Office Communicator 2007 R2


For an immediate fix, terminate the pegged OCS processes on the XenApp server(s) where users are not able to log off, this instantly fixes the issue for all other users logged on the server.

The permanent solution is to apply this fix (2755391) from Microsoft, however head over and read this article to get more information on the issue.

Original post at the Citrix knowledgebase.