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When you try to log on to Outlook Web App or Exchange Control Panel (ECP), you receive the following error message:

Sorry, something went wrong
An error has occurred on the server.

If you click the TECHNICAL DETAILS link, the following text is displayed:

An unexpected error occurred and your request couldn't be handled.
X-OWA-Error: System.NullReferenceException
X-OWA-Version: OWA Version
X-FEServer: Exchange 2013 Client Access Server
X-BEServer: Exchange 2013 Mailbox Server
Date: Date and Time
Note This behavior occurs even though you can still use Microsoft Outlook to send and receive email messages.


The GUID value is stored in the browser cookie collection and is included in an Outlook Web App or ECP request. If the GUID value that's stored in Active Directory Domain Services (AD DS) doesn't match, the server blocks the request.


To fix this issue, install Cumulative Update 11 or a later cumulative update for Exchange Server 2013.

Note This update enables periodic recycle of the Outlook Web App or ECP app pools (every 14 days). If you disable this recycle functionality or set the period to more than 28 days, the issue may recur.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

When this issue occurs, the Application log in Event Viewer may show the following events:

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