Symptoms
When you join a meeting from a different organization that's federated with your organization through a meeting link in Microsoft Skype for Business 2015 (Lync 2013), you can't join the meeting anonymously, and you receive a 403 forbidden error together with a 1034 diagnostic message. This occurs if the meeting organizer is disabled for external connection (federation).
Resolution
To fix this issue, install the November 7, 2017, update (KB4011255) for Skype for Business 2015 (Lync 2013).
Note Lync 2013 was upgraded to Skype for Business in April 2015.
