OWA application pool crashes with KeyNotFound exception in Exchange Server 2013

Applies to: Exchange Server 2013 EnterpriseExchange Server 2013 Standard Edition


In a Microsoft Exchange Server 2013 environment, the OWA application pool crashes several times a day. In this situation, the following event is logged:


This issue occurs because Exchange Server expects all meeting participants to be rendered. However, for some special meetings, some participants may not be rendered successfully. When this issue occurs, a KeyNotFound exception is displayed, and the OWA application pool crashes.


To fix this issue, install Cumulative Update 13 for Exchange Server 2013 or a later cumulative update for Exchange Server 2013.


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


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