Lync Server 2010Lync Server 2013Skype for Business Server 2015

Conferencing modalities no longer function in Lync Server 2010, Lync Server 2013, or Skype for Business Server 2015 after you install Security Bulletin MS16-065

Gulab Prasad · · 1 min read

This problem occurs because an information disclosure vulnerability exists in the Transport Layer Security protocol and the Secure Sockets Layer protocol (TLS/SSL) as they are implemented in the encryption component of the Microsoft .NET Framework. An attacker who successfully exploits this vulnerability can decrypt encrypted TLS/SSL traffic.
Here is the resolutions...
https://support.microsoft.com/en-us/kb/3165438 
Cheers,
Gulab Prasad