Microsoft Office Communicator Web Access (CWA) Application Sharing does not work for internal users. For example, CWA internal users cannot share the desktop in a conference.
This problem occurs because a CWA client tries to resolve the external address of the media relay while sharing the desktop in a conference. In some topologies, DNS resolution takes a long time. This behavior causes the sharing to time out for 15 seconds.
To resolve this issue, apply the following update:
975614 Description of the cumulative update package for Office Communications Server 2007 R2, Communicator Web Access: April 2010
To work around this issue, reduce the time for DNS query failures in the network topology, specifically for external address of the media relay.