Assume that a Microsoft Lync Web App user joins an online meeting through a Unified Access Gateway (UAG) gateway. In this situation, the user cannot download the shared contents and images that are shared on a whiteboard in the meeting.
This issue occurs because the Lync Web App sends a HTTP GET request to retrieve the shared file. However, the request does not contain the session cookies which define the session context. Therefore, the UAG gateway does not recognize the meeting session when the gateway receives the request. Because of this behavior, the gateway sends a response to Lync Web App to prompt that the file cannot be downloaded.
To resolve this issue, install the following cumulative update:
2514979 Description of the cumulative update package for Lync Server 2010, Web Components Server: November 2011