When you use Microsoft Skype for Business clients in Windows Server 2012 R2, you may experience authentication failures.


This issue occurs because of a deadlock in Windows Local Security Authority Subsystem Service (LSASS) in Windows Server 2012 R2. The deadlock causes perceived lockup of the server in which all incoming server-to-server TLS negotiations fail and authentication requests from Skype for Business clients fail.


To fix this issue, install the July 18, 2017, rollup update (KB4025335) for Windows Server 2012 R2.

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