You run a Microsoft Unified Communications Managed API (UCMA) endpoint on a Lync Server 2010 server. In this situation, you might find the following call flow in the trace log during a blind transfer that involves an UCMA endpoint:
The UCMA client sends a REFER message to the Mediation server.
The Mediation server accepts the REFER message, and then tries to transfer the calls.
The UCMA client sends a SUBSCRIBE message to end the REFER subscription.
The Mediation server sends the NOTIFY message that contains a 200 OK event on the ended REFER subscription.
The call is ended.
Note Generally, the Mediation server should not try to send the NOTIFY message on an ended subscription.
This issue occurs because the Mediation server ignores the SubscriptionTerminated event. Therefore, an exception is caused when the NOTIFY message is sent, and then the call is ended.
To resolve this issue, install the following cumulative update:
2640253 Description of the cumulative update for Lync Server 2010, Mediation Server: November 2011