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Assume that you have mailboxes that have issues with the logical index in their mailbox database. When you try to use the move, restore, or repair operation on the mailboxes, the Store Worker process may stop responding randomly, and you receive the following error message:

System.NullReferenceExceptions" at "Microsoft.Exchange.Server.Storage.LazyIndexing.LogicalIndex..ctor

Additionally, the following event is recorded in the Application event log:

Log Name:      Application
Source:        MSExchange Common
Event ID:      4999
Task Category: General
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      XXX
Watson report about to be sent for process id: 20056, with parameters: E12, c-RTL-AMD64, 15.01.1261.035, M.E.Store.Worker, M.E.S.Storage.LazyIndexing, M.E.S.S.L.LogicalIndex..ctor, System.NullReferenceException, 1b58-dumptidset, 15.01.1261.035.
ErrorReportingEnabled: False


This issue occurs because the lazy indexes of the mailbox can't be loaded successfully. This causes the Store Worker process to crash.

Note These lazy indexes are different from the context indexes that are built and maintained by the Microsoft Exchange Search service, as they are part of the Mailbox database.


Exchange Server 2016

To resolve this issue, install Cumulative Update 9 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.


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


Learn about the terminology that Microsoft uses to describe software updates.

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