This issue occurs in a Microsoft Lync Server 2013 environment when you try to share your desktop in an online meeting, and the meeting attendees include a group that has a large number of users (such as 50).
When this issue occurs, the desktop-sharing attempt fails. Additionally, the following diagnostic message is displayed in the Call Detail Report (CDR) report:
New sharer joined the conference
To fix this issue, install the April 2016 cumulative update 5.0.8308.956 for the Lync Server 2013, Core Components.
To work around this issue, create a new meeting, and then let all the participants join the new one.