You select the Do not join audio option in the Join Meeting Audio dialog box when you join a Microsoft Lync 2010 conference as an organizer.
You click Invite by name or phone number in People Options, or you drag the user from the contact list to the meeting dialog box to invite a user to the conference.
In this scenario, the user who you invite does not receive the invitation of the conference.
This issue occurs because a flag is not set when you select the Do not join audio option. Therefore, an AppInvite message is not sent. The flag triggers the behavior that the Lync 2010 application layer adds audio modality to the AppInvite message when you join a conference without any modalities.
To resolve this issue, install the following cumulative update:
2571543 Description of the cumulative update package for Lync 2010: July 2011
If the Join Meeting Audio dialog does not appear, you can follow these steps to change the default audio choice.
Start the Lync 2010 client, and then click the Options button.
Click Phones in the Lync-Options dialog box.
Under Joining conference calls, in the Join meeting audio from box, select Do not join audio.