Symptoms
When you open a conversation that doesn't have audio in Microsoft Skype for Business 2016. The Hotkey process doesn't check if the audio is connected before you try to mute or unmute. As a result, the conversation shows an error alert and flashes the frame.
Resolution
To fix this issue, install the December 6, 2016, update (KB3127980) for Skype for Business 2016.
