Consider the following scenario:
You sign in to Microsoft Lync 2010 for iPad.
You switch to the chats window by clicking the Chats icon in the tab bar.
There is one conversation in the list of conversations in the chats window.
You click the Edit button, click the Action button, and then click the Delete Conversation button.
In this scenario, a red circle is displayed in the list of conversations, and the Select All and Delete buttons are displayed at the bottom of the chats window. Additionally, if you click the Select All button, Lync 2010 stops responding.
To resolve this issue, install the following cumulative update:
2673225 Description of the cumulative update package for Lync 2010 for iPad: March 2012