Consider the following scenario. You use a user account to sign in to Windows. Then, you sign in to Microsoft Lync 2010 by using a different account. In this scenario, you are unexpectedly prompted for credentials when you sign in to the Lync Online service.
Note The user account that you used to sign in to Windows was previously used to sign in to the Lync Online service successfully.
This issue occurs because online identity is not retrieved automatically across different accounts.
To work around this issue, sign in to Lync 2010 by using the same user account as the Windows logon account.