Encountered an error while attempting to perform an LDAP search for all Lync Server attributes on a user object. The error ...

Encountered an error while attempting to perform an LDAP search for all Lync Server attributes on a user object.  The error was serious enough to warrant stopping synchronization, which means that if this error is not corrected, no more user updates will be pulled from AD and into the Lync Server database.

User object: %1  Error: %2, (%3)
Cause: This event occurs for a variety of reasons. The most common are either the domain controllers going down, or the server running out of memory.
Resolution:
Check for failures in the domain infrastructure. Because the User Replicator automatically retries the operation, when the error is resolved, the User Replicator will automatically start synchronizing again.