This issue occurs in the following scenario:
- A user applies the March 10, 2015 update (KB2956174) or a later version of update for Microsoft Lync 2013 (Microsoft Skype for Business) April 14, 2015 update (KB2889923) or May 12, 2015, security update (KB 3039779).
- The user is in an environment that has both an HTTP proxy server and an Edge server deployed.
- The user joins an online meeting that is created in a non-federated environment.