The following error occurs:

Event id: 64
Event Source: MSExchange OWA
Description: Failed to read and update the Outlook Web Access configuration settings. Virtual directory: “Virtual_Directory_Name”. Web site: “Web_Site_Name”. Error message: “Error_Message”

This error indicates that Microsoft Outlook Web Access did not read and update its configuration settings from the Active Directory directory service for the Outlook Web Access virtual directory and Internet Information Services (IIS) Web site specified in the event description.

On the Client Access Server which has this problem you can do the following in the Exchange powershell :

Make sure you have a backup of all your settings, IIS Metabase etc.

First retrieve the identity of the Virtual Directory you want to remove.
In this case we use the “owa (default web site)” on the server SERVER01.

remove-OWAVirtualDirectory -identity “SERVER01\owa (default web site)”

After this has been removed, create a new OWA virtual directory by running this on the CAS where it has to be created :

new-OWAVirtualDirectory “owa (default web site)”

After it is created OWA should be working already. Make sure you set the settings back to their original values. More information : KB Article 930864