Symptoms
You cannot sign in to the Microsoft Skype for Business 2015 (Lync 2013) client because of the RTC_E_INVALID_OBJECT_STATE error.
Resolution
To fix this issue, install the December 6, 2016, update (KB3127976) for Skype for Business 2015 (Lync 2013).
Note Lync 2013 was upgraded to Skype for Business in April 2015.