Microsoft Communicator ... This update resolves an issue that causes Microsoft Communicator for Mac 2011 running on OS X 10.7 Lion to crash when you send an IM or start an audio call or a visual call.
What's new in Microsoft Communicator
This update fixes critical issues in Communicator for Mac, including issues that might cause Communicator to stop responding or quit unexpectedly. The Microsoft Communicator for Mac 2011 13.1.3 Update adds support for Juniper and Cisco VPN clients. This update also fixes an issue with the ServerAddressInternal managed preference setting.