Assume that you start an instant message conversation by using Lync for Mac 2011 in a network. Then Lync for Mac 2011 disconnects from the network. In this situation, the instant message conversation window closes unexpectedly.
Note Lync for Mac 2011 might disconnect from the network because of network outage or because the computer sleeps.
To resolve this issue, install the following cumulative update:
2909662 Description of the Microsoft Lync for Mac 2011 14.0.7 update