Assume that audio and video are disabled in your conference policy settings. When you try to share your desktop during an online meeting with external users who aren't federated with your company, these users have no indication that the desktop is shared with them in Microsoft Lync 2013.
Resolution
To fix this issue, install the December 8, 2015 security update (KB3114351) for Lync 2013 (Skype for Business).
Note Lync 2013 was upgraded to Skype for Business in April 2015.
