I always find it hard to explain customers when “ERROR” level events are expected, it smells like teen spirit and buggy code. This is one of these expected errors seen is many LYNC environments, due to the fact a lot of customers are still running Exchange 2010
But finally this is now in the past.
The latest and greatest CU for LYNC 2013 has this bug fixed among others
The KB describing this specific error
The article describing the CU Feb 2015 in general
For deloyment please see my other articles on LYNC Cumulative updates, the process is exactly the same – and since Microsoft are so clever to utilize the same link for CU – the links are even reusable – nice 🙂