On a Microsoft Lync Server 2010 front-end server, client users may experience the following symptoms:

  • New users cannot sign in to the front-end server.

  • Users cannot complete instant message conversations.

  • Users cannot join meetings that are hosted on the front-end server.

Additionally, the Front End (FE) service (Rtcsrv.exe) uses more CPU resources than expected.


This issue occurs because of a race condition in the rtcsrv.exe process.


To fix this issue, install the April, 2016 Cumulative Update 4.0.7577.728 for Lync Server 2010.

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