After a user enters his or her account name and password in Outlook Web App, the logon process fails, and the user receives a time-out error message. When this issue occurs, no Outlook Web App users in your Exchange Server organization can log on. This issue may last for several hours until you restart the Client Access server.
This issue occurs because of an infinite wait (or freeze) in the ADNotificationListener method.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.