Consider the following scenario:
You sign in to a Microsoft Lync 2010 organization that has a cumulative update for Lync 2010 installed. The cumulative update was released in November 2011 or later.
You receive a Lync Online meeting invitation from a user in another Lync Server 2010 organization. The Lync Server 2010 organization is non-federated.
The Dynamic Host Configuration Protocol (DHCP) option is configured to reply to DHCP 120 queries in your organization.
You try to join a Lync Online meeting.
In this scenario, you cannot join the meeting.
This issue occurs because the automatic discovery process of the Lync 2010 client incorrectly uses the local SIP server that is returned by the DHCP server when you try to join the meeting.
To resolve this issue, install the following cumulative update:
2791382 Description of the cumulative update package for Lync 2010: March 2013
For more information about how to set up DHCP for devices, go to the following Microsoft website:
How to set up DHCP for devices For more information about the cumulative update for Lync 2010 that is dated November 2011, click the following article number to view the article in the Microsoft Knowledge Base:
2514982 Description of the cumulative update package for Lync 2010: November 2011 For more information about Lync 2010 client administration, download the following guide from the Microsoft Download Center: