- You sign in to Microsoft Lync 2010 in a Lync Server 2010 environment that has the cumulative update for Lync Server 2010 that was released in February 2012 installed.
- Anonymous user access is enabled in the environment.
- You create a Lync Online meeting.
- You invite a Lync 2010 user to join the meeting. The user's Lync 2010 client has the cumulative update for Lync 2010 that was released in April 2011 or a later cumulative update installed. Additionally, the user is in a Lync Server 2010 organization that is not federated with your organization.