Recently I came across a small problem when I tried to move Lync users between pools in different sites. The environment is Lync 2013 Enterprise Edition with full HA and HLB(Riverbed Stingray).
The Error was “Unable to connect to some of the servers in pool <name> due to a Distributed Component Object Model (DCOM) error”.
All servers in the solution is Windows Server 2012/R2 running Lync 2013 Enterprise Edition.
Ben Lee posted an article abut the same error message in 2011, and the article is also valid for a Lync2013-only environment. The article can be found here.
PS: Make sure the HLB is configured correctly to handle all Lync traffic.
Universal Communications, My experiences. 