When a user joins a Skype for Business meeting of a different organization that is not federated with the user's organization, the Skype for Business client fails to perform anonymous fallback. In this situation, the meeting join process fails and the user sees a blank conversation window.
This issue occurs because of a change that was made in the July 5, 2016, update (KB3115261) for Lync 2013 (Skype for Business) and in some Current Channel Click-to-Run builds of Skype for Business 2016.
Lync 2013 (Skype for Business)
This issue is fixed for Lync 2013 (Skype for Business) MSI-based clients. For more information, see the following Microsoft Knowledge Base article:
Anonymous meeting join fails in Lync 2013 (Skype for Business)
This issue is fixed for Lync 2013 (Skype for Business) Click-to-Run installations, starting in Office build 15.0.4841.1002.
For more information about how to check your Office installation build and to update your Click-to-Run Office installation on demand, see the following Microsoft Support article:
Skype for Business 2016
This issue is fixed for Skype for Business 2016 Click-to-Run installations, starting in Office build 16.0.7070.2033. If the build number is earlier than 16.0.7070, that build is not affected.
Note Skype for Business 2016 MSI-based installations are not affected by this issue.
To determine whether your Office installation is Click-to-Run or MSI-based, follow these steps:
Start an Office 2016 application.
On the File menu, select Account.
For Office 2016 Click-to-Run installations, an Update Options item is displayed. For MSI-based installations, the Update Options item isn't displayed.
Office 2016 Click-to-Run installation
MSI-based Office 2016
To join an external company meeting that is not federated, use one of the following methods.
Use Skype for Business Web App. To do this, see the "Join with Skype for Business Web App if Skype for Business desktop is installed" section of the following Office website:
Roll back the installation.
For MSI-based installations, roll back to the June 2016 update (KB3115033) until a fix is made available for this issue.
To roll back Click-to-Run installations, see the following Knowledge Base article:
2770432 How to revert to an earlier version of Office 2013 or Office 2016 Click-to-Run
Microsoft is aware of this issue in Skype for Business 2016 and will post more information in this article when it becomes available.