Assume that you have an Office 365 account, and then you change the password of the account to have more than 16 characters. In this situation, you cannot sign in to Microsoft Lync for Mac 2011 by using the account.
To resolve this issue, install the following cumulative update:
2909662 Description of the Microsoft Lync for Mac 2011 14.0.7 update
Article ID: 2913469 - Last Review: 12 Dec 2013 - Revision: 1