Address Book Server was unable to perform its heartbeat function against the back-end database after 3 attempts. SQL Connection ...

Address Book Server was unable to perform its heartbeat function against the back-end database after 3 attempts.

SQL Connection String: %1
Exception: %2
Cause: SQL Connectivity issues.
Resolution:
Verify that the RTCService account has access to the database and that the machine running the Lync Server Front-End service has connectivity to the back-end server.