Users must manually input the user name every time that the user signs in to the Microsoft Lync 2010 client. This issue occurs when the following conditions are true:
The computer that is running the Lync 2010 client does not join a domain that has Microsoft Lync Server 2010 deployed.
The sign-in address and the user name are not the same. For example, the sign-in address is "email@example.com" and the user name is "DOMAIN\123."
The Save my password check box is not selected.
The update that is described in the Microsoft Knowledge Base (KB) article 2670498 is installed on the computer that is running the Lync 2010 client.
This issue occurs because the function that is used to retrieve the sign-in information about the user does not obtain a correct value after KB 2670498 is installed.
To resolve this issue, install the following cumulative update:
2670326 Description of the cumulative update for Lync 2010: February 2012